fix Makefile and README.md for 2000/bmeyer
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@@ -1,215 +1,329 @@
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#!/bin/make
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#!/usr/bin/env make
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# 2000 makefile
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#
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#
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# Copyright (C) Simon Cooper, Landon Curt Noll, Peter Seebach
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# IOCCC 2000 winning entry - bmeyer
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# and Leonid A. Broukhis, 2000.
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# All Rights Reserved. Permission for personal, educational or non-profit
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# use is granted provided this this copyright and notice are included in its
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# entirety and remains unaltered. All other uses must receive prior permission
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# from the contest judges.
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SHELL= /bin/sh
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################################################################################
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CAT= cat
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RM= rm
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SED= sed
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TRUE= true
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#CINCLUDE= -I ${HOMEBREW_PREFIX}/include/SDL2
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# optimization
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#
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#
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||||||
# Most compiles will safely use -O2. Some can use only -O.
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# Regarding individual entries:
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||||||
# A few compilers have broken optimizers and thus you may
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#
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||||||
# not want anything.
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# IOCCC winning entry code may not work on your system. Even with standards,
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# conditions and build environments change, especially when it comes to more
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# extreme code such you might find in an IOCCC winner. Moreover, what was
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# allowed and liked in one IOCCC contest may no longer be liked/allowed in
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# later IOCCC years.
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#
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# Corrections on winning author and fixing typos in remarks are VERY WELCOME.
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#
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# GitHub pull requests are welcome:
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#
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# If you have a patch that might make running an entry work in modern Unix-like
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# environments, please create a GitHub pull request for the IOCCC judges to
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# consider.
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#
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# Suggestions and corrections regarding Makefiles, winning author information,
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# fixing typos in remarks, and code patches are welcome via opening a GitHub
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# issue or better yet, by creating a GitHub pull request for the IOCCC judges
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# to consider. To form a GitHub issue or GitHub pull, please visit:
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#
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# https://github.com/ioccc-src/winner
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#
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################################################################################
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# This work by Landon Curt Noll and Leonid A. Broukhis is licensed under:
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#
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# Creative Commons Attribution-ShareAlike 3.0 Unported License.
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#
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# See: http://creativecommons.org/licenses/by-sa/3.0/
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#############################
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# shell used by this Makefile
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#############################
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#
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SHELL= bash
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#######################
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# common tool locations
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#######################
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#
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include ../../var.mk
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# Set X11_LIBDIR to the directory where the X11 library resides
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#
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#X11_LIBDIR= /usr/X11R6/lib
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#X11_LIBDIR= /usr/X11/lib
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X11_LIBDIR= /opt/X11/lib
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# Set X11_INCLUDEDIR to the directory where the X11 include files reside
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#
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#X11_INCDIR= /usr/X11R6/include
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#X11_INCDIR= /usr/X11/include
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X11_INCDIR= /opt/X11/include
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# Common C compiler warnings to silence
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#
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#CSILENCE=
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CSILENCE= -Wno-format -Wno-parentheses -Wno-string-plus-int
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# Common C compiler warning flags
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#
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#CWARN= ${CSILENCE}
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#CWARN= -Wall ${CSILENCE}
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#CWARN= -Wall -Wextra ${CSILENCE}
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CWARN= -Wall -Wextra -pedantic ${CSILENCE}
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# Compiler standard
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#
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#CSTD=
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#CSTD= -ansi
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CSTD= -std=gnu99
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# Compiler bit architecture
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#
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# Some entries require 32-bitness:
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# ARCH= -m32
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#
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# Some entries require 64-bitness:
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# ARCH= -m64
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#
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# By default we assume nothing:
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#
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ARCH=
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# Defines that are needed to compile
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#
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#CDEFINE=
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CDEFINE= -DY=
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# Include files that are needed to compile
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#
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CINCLUDE=
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#CINCLUDE= -include stdlib.h
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#CINCLUDE= -include stdio.h
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#CINCLUDE= -include stdlib.h -include stdio.h
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#CINCLUDE= -I ${X11_INCDIR}
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#CINCLUDE= `${SDL2_CONFIG} --cflags`
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# Optimization
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#
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# Most compiles will safely use -O2. Some can use only -O1 or -O.
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# A few compilers have broken optimizers or this entry make break
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# under those buggy optimizers and thus you may not want anything.
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# Reasonable compilers will allow for -O3.
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#
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#
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#OPT=
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#OPT=
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#OPT= -O
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#OPT= -O
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OPT= -O2
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#OPT= -O1
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#OPT= -O2
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OPT= -O3
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# flags for ANSI compiles
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# Default flags for ANSI C compilation
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#
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#
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# NOTE: Some ANSI compilers make use of -Xa to turn on ANSI mode,
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CFLAGS= ${CSTD} ${CWARN} ${ARCH} ${CDEFINE} ${CINCLUDE} ${OPT}
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# others such as gcc may want -ansi, others (Compaq Tru64 Unix)
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# want -std1, and others may want nothing at all.
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# Adjust the CFLAGS line as needed.
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#
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# NOTE: Some compilers cannot optimize, or optimize some entries
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# incorrectly. You might want to turn on -O to see if your
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# compiler can handle them.
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#
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#
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#CFLAGS= -Xa ${OPT}
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#CFLAGS= -std1 $(OPT)
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CFLAGS= -ansi ${OPT}
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NO_ANSI_CFLAGS=
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# Libraries needed to build
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#NO_ANSI_CFLAGS=
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#
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#LIBS=
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LIBS= -lm
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#LIBS= -L ${X11_LIBDIR} -lX11
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#LIBS= `${SDL2_CONFIG} --libs`
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# NOTE: On some systems, the library path does not include the location
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# C compiler to use
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# of the X11 libraries. You might need to use a -L/path/to/X11/lib/dir
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# in order to compile with these libs.
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#
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X11CCFLAGS= -I/usr/X11R6/include -I/usr/X11R6/include/X11 -I/usr/include/X11
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#X11CCFLAGS=
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X11LDFLAGS= -L/usr/X11R6/lib
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#X11LDFLAGS=
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# Perl
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#
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PERL= perl
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#PERL= perl5
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# ANSI compiler
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#
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# Set CC to the name of your ANSI compiler.
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#
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# Some entries seem to need gcc. If you have gcc, set
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# both CC and MAY_NEED_GCC to gcc.
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#
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# If you do not have gcc, set CC to the name of your ANSI compiler, and
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# set MAY_NEED_GCC to either ${CC} (and hope for the best) or to just :
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# to disable such programs.
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#
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#
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CC= cc
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CC= cc
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MAY_NEED_GCC= gcc
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#CC=clang
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#CC=gcc
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# winners that compile under ANSI C
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# Compiler add-ons or replacements for clang only
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#
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#
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WINNERS= anderson schneiderwent primenum bellard bmeyer briddlebane dhyang \
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ifeq ($(CC),clang)
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dmy2jd jarijyrki dlowe natori rince robison thadgavin tomx
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ALT_NAMES= schneiderwent.orig briddlebane.orig thadgavin.orig
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DATA_FILES= schneiderwent_files bmeyer_files jarijyrki_files
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all: ${WINNERS}
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# Best use of flags
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#
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#
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anderson: anderson.c
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CSILENCE+= -Wno-comma -Wno-disabled-macro-expansion -Wno-float-conversion \
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${CC} ${CFLAGS} $? -o $@
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-Wno-format-nonliteral -Wno-missing-prototypes \
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-Wno-missing-variable-declarations -Wno-poison-system-directories \
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# Most Timely Output
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-Wno-shadow -Wno-shorten-64-to-32 -Wno-sign-conversion \
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-Wno-strict-prototypes
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#
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#
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schneiderwent: schneiderwent.c
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CWARN+= -Weverything
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${CC} ${CFLAGS} $? -o $@
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schneiderwent_files: schneiderwent.data
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schneiderwent.orig: schneiderwent.orig.c
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${CC} ${CFLAGS} $? -o $@
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# Best Abuse of CPP
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#
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#
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primenum: primenum.c
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endif
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${CC} ${CFLAGS} $? -o $@
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# Most Specific Output
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# Specific add-ons or replacements for gcc only
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#
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#
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bellard: bellard.c
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ifeq ($(CC),gcc)
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${CC} ${CFLAGS} $? -o $@
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#
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#CSILENCE+=
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#
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#CWARN+=
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#
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endif
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# Best Utility
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#
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# machines operating in 64 bit mode:
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#
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bmeyer: bmeyer.c
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${CC} -DY= -O6 $? -o $@ -lm
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#
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# linux/x86, glibc 2.0, libc4/5:
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#
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# bmeyer: bmeyer.c
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# ${CC} -DY="__setfpucw(0x127f)" -O6 $? -o $@ -lm
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#
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||||||
# linux/x86, glibc 2.1:
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#
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# bmeyer: bmeyer.c
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# ${MAY_NEED_GCC} -DY='int x=0x127f; __asm__ ("fldcw %0" : : "m" (*&x))' \
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# -O6 $? -o $@ -lm
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bmeyer_files: lavabus.pgm lenna.glic michael.pgm
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##############################
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# Special flags for this entry
|
||||||
# Best Abuse of User
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##############################
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||||||
#
|
#
|
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briddlebane: briddlebane.c
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ENTRY= bmeyer
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${CC} ${CFLAGS} $? -o $@ -lm
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PROG= ${ENTRY}
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||||||
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|
||||||
briddlebane.orig: briddlebane.orig.c
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|
||||||
${CC} ${CFLAGS} $? -o $@ -lm
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# Best Layout
|
|
||||||
#
|
#
|
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dhyang: dhyang.c
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OBJ= ${PROG}.o
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${CC} ${CFLAGS} $? -o $@
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DATA= lavabus.pgm lenna.glic michael.pgm
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TARGET= ${PROG}
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dmy2jd: dmy2jd.c
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${CC} ${CFLAGS} $? -o $@
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|
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# Best of Show
|
|
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#
|
#
|
||||||
jarijyrki: jarijyrki.c
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ALT_OBJ=
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${CC} ${X11CCFLAGS} ${CFLAGS} -DNeedFunctionPrototypes \
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ALT_TARGET=
|
||||||
-DU=40 -DT=98 '-Dz=(T+1)*U*U' -DQ=80 -DS=20 -DN=10 -DB=5 -DG=23 \
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|
||||||
-Dp=7 '-DM=((p+1)*Q)+S' '-DH=(G*S)+S+S' -DC=XK_Up -DL=XK_Down \
|
|
||||||
-DO=XK_Left -DV=XK_Right -DR=XK_Escape -D_=XK_BackSpace \
|
|
||||||
$? -o $@ ${X11LDFLAGS} -lX11
|
|
||||||
|
|
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jarijyrki_files: sheet1.info
|
|
||||||
|
|
||||||
# Worst Abuse of the Rules
|
#################
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||||||
|
# build the entry
|
||||||
|
#################
|
||||||
#
|
#
|
||||||
# NOTE: You will need to adjust this path to the place where Perl has been
|
all: data ${TARGET}
|
||||||
# installed on your system. Running "perl -V" may help you locate
|
|
||||||
# this place.
|
|
||||||
#
|
|
||||||
# The following bit of perl may help determining the values you need:
|
|
||||||
#
|
|
||||||
# perl -MConfig -e 'print "$Config{archlibexp}/CORE\n"'
|
|
||||||
#
|
|
||||||
#
|
|
||||||
dlowe: dlowe.c
|
|
||||||
${CC} ${NO_ANSI_CFLAGS} -DPERL_POLLUTE \
|
|
||||||
`${PERL} -MExtUtils::Embed -e ccopts` $? -o $@ \
|
|
||||||
`${PERL} -MExtUtils::Embed -e ldopts`
|
|
||||||
|
|
||||||
# Best Small Program
|
|
||||||
#
|
|
||||||
natori: natori.c
|
|
||||||
${CC} ${CFLAGS} $? -o $@ -lm
|
|
||||||
|
|
||||||
# Astronomically Obfuscated
|
|
||||||
#
|
|
||||||
rince: rince.c
|
|
||||||
${CC} ${X11CCFLAGS} ${CFLAGS} -DM_PI=3.14159265358979323846 \
|
|
||||||
$? -o $@ -lm ${X11LDFLAGS} -lX11
|
|
||||||
|
|
||||||
# Best game
|
|
||||||
#
|
|
||||||
robison: robison.c
|
|
||||||
${CC} ${CFLAGS} $? -o $@
|
|
||||||
|
|
||||||
# Most Portable Output
|
|
||||||
#
|
|
||||||
thadgavin: thadgavin.c
|
|
||||||
${CC} ${CFLAGS} $? -o $@ -lcurses -lm
|
|
||||||
|
|
||||||
thadgavin.orig: thadgavin.orig.c
|
|
||||||
${CC} ${CFLAGS} $? -o $@ -lncurses -lm
|
|
||||||
|
|
||||||
# Most Complete Program
|
|
||||||
#
|
|
||||||
tomx: tomx.c
|
|
||||||
${CC} ${CFLAGS} $? -o $@
|
|
||||||
|
|
||||||
everything: ${WINNERS} ${ALT_NAMES} ${DATA_FILES}
|
|
||||||
|
|
||||||
clean:
|
|
||||||
${RM} -f *.o a.out core ${WINNERS}
|
|
||||||
|
|
||||||
clobber: clean
|
|
||||||
${RM} -f ${WINNERS}
|
|
||||||
${RM} -f ${ALT_NAMES}
|
|
||||||
|
|
||||||
nuke: clobber
|
|
||||||
@${TRUE}
|
@${TRUE}
|
||||||
|
|
||||||
install: all
|
.PHONY: all alt data everything clean clobber install \
|
||||||
${CAT} ${WINNERS} ${ALT_NAMES} > /dev/null
|
love haste waste maker easter_egg sandwich \
|
||||||
|
supernova deep_magic magic charon pluto
|
||||||
|
|
||||||
|
${PROG}: ${PROG}.c
|
||||||
|
${CC} ${CFLAGS} $< -o $@ ${LIBS}
|
||||||
|
|
||||||
|
# alternative executable
|
||||||
|
#
|
||||||
|
alt: data ${ALT_TARGET}
|
||||||
|
@${TRUE}
|
||||||
|
|
||||||
|
# data files
|
||||||
|
#
|
||||||
|
data: ${DATA}
|
||||||
|
@${TRUE}
|
||||||
|
|
||||||
|
# both all and alt
|
||||||
|
#
|
||||||
|
everything: all alt
|
||||||
|
|
||||||
|
|
||||||
|
###############
|
||||||
|
# utility rules
|
||||||
|
###############
|
||||||
|
#
|
||||||
|
clean:
|
||||||
|
${RM} -f ${OBJ} ${ALT_OBJ}
|
||||||
|
@-if [ -f indent.c ]; then \
|
||||||
|
echo ${RM} -f indent.c; \
|
||||||
|
${RM} -f indent.c; \
|
||||||
|
fi
|
||||||
|
|
||||||
|
clobber: clean
|
||||||
|
${RM} -f ${TARGET} ${ALT_TARGET}
|
||||||
|
@-if [ -e sandwich ]; then \
|
||||||
|
${RM} -f sandwich; \
|
||||||
|
echo 'ate sandwich'; \
|
||||||
|
fi
|
||||||
|
|
||||||
|
install:
|
||||||
|
@echo "Dr. Spock says that is not logical!"
|
||||||
|
@${TRUE}
|
||||||
|
|
||||||
|
# you may be able to misunderstand the source by reading indent.c
|
||||||
|
#
|
||||||
|
indent.c: ${PROG}.c
|
||||||
|
@if which "${GINDENT}" >/dev/null 2>&1; then \
|
||||||
|
echo ${RM} -f $@; \
|
||||||
|
${RM} -f $@; \
|
||||||
|
echo "${GINDENT} < $< > $@"; \
|
||||||
|
${GINDENT} < $< > $@; \
|
||||||
|
elif which "${INDENT}" >/dev/null 2>&1; then \
|
||||||
|
echo ${RM} -f $@; \
|
||||||
|
${RM} -f $@; \
|
||||||
|
echo "${INDENT} < $< > $@"; \
|
||||||
|
${INDENT} < $< > $@; \
|
||||||
|
else \
|
||||||
|
echo "no intent tool found, ident $< yourself, sorry"; \
|
||||||
|
echo "exit 1"; \
|
||||||
|
exit 1; \
|
||||||
|
fi
|
||||||
|
|
||||||
|
|
||||||
|
##################
|
||||||
|
# 133t hacker rulz
|
||||||
|
##################
|
||||||
|
#
|
||||||
|
love:
|
||||||
|
@echo 'not war?'
|
||||||
|
@${TRUE}
|
||||||
|
|
||||||
|
haste:
|
||||||
|
$(MAKE) waste
|
||||||
|
@${TRUE}
|
||||||
|
|
||||||
|
waste:
|
||||||
|
@echo 'haste'
|
||||||
|
@${TRUE}
|
||||||
|
|
||||||
|
maker:
|
||||||
|
@echo 'Participate in a maker faire'
|
||||||
|
@${TRUE}
|
||||||
|
|
||||||
|
easter_egg:
|
||||||
|
@echo "you expected to often misunderstand this $${RANDOM} magic"
|
||||||
|
@echo "chongo '<was here>' /\\oo/\\"
|
||||||
|
@echo "Eggy"
|
||||||
|
|
||||||
|
sandwich: easter_egg
|
||||||
|
@if [ `id -u` -eq 0 ]; then \
|
||||||
|
echo 'Okay.'; \
|
||||||
|
echo "$${RANDOM}`date +%s`$${RANDOM}" > $@; \
|
||||||
|
else \
|
||||||
|
echo 'What? Make it yourself.'; \
|
||||||
|
exit 1; \
|
||||||
|
fi
|
||||||
|
|
||||||
|
# Understand the history of the Homebrew Computer Club
|
||||||
|
# as well as the West Coast Computer Faire and
|
||||||
|
# you might be confused different. :-)
|
||||||
|
#
|
||||||
|
supernova: sandwich
|
||||||
|
@-if [ -r .code_anal ]; then \
|
||||||
|
${RM} -f .code_anal_v6; \
|
||||||
|
else \
|
||||||
|
echo "planet deniers, like some members of the IAU, are so cute when they try to defend their logic"; \
|
||||||
|
fi
|
||||||
|
@echo "A $@ helps ${MAKE} the elements that help form planets"
|
||||||
|
@${TRUE}
|
||||||
|
|
||||||
|
deep_magic: supernova
|
||||||
|
@-if [ -r .code_anal ]; then \
|
||||||
|
ccode_analysis --deep_magic 7889066cdbdf09b0408021754586e895be641cc9be29e7eafd3ca65359541f17 \
|
||||||
|
--FNV1a_hash_512_bit -v2 "${PROG}" "${PROG}.c"; \
|
||||||
|
else \
|
||||||
|
echo "Wrong! Do it again!"; \
|
||||||
|
sleep 2; \
|
||||||
|
echo "Wrong! Do it again!"; \
|
||||||
|
sleep 2; \
|
||||||
|
echo "Wrong! Do it again!"; \
|
||||||
|
fi
|
||||||
|
@${TRUE}
|
||||||
|
|
||||||
|
magic: deep_magic
|
||||||
|
@-if [ -r .code_anal ]; then \
|
||||||
|
ccode_analysis --level 20003 --mode 5717175 --FNV1a_hash_512_bit -v2 "${PROG}" "${PROG}.c"; \
|
||||||
|
else \
|
||||||
|
echo "If you don't eat yer meat, you can't have any pudding!"; \
|
||||||
|
echo "How can you have any pudding if you don't eat yer meat?!"; \
|
||||||
|
fi
|
||||||
|
@${TRUE}
|
||||||
|
|
||||||
|
# The IOCCC resident astronomer states
|
||||||
|
#
|
||||||
|
charon: magic
|
||||||
|
@echo "$@ is a dwarf planet"
|
||||||
|
@echo "dwarf is a type of planet"
|
||||||
|
@echo "therefore IAU, $@ is a planet"
|
||||||
|
|
||||||
|
pluto: charon
|
||||||
|
${MAKE} charon
|
||||||
|
@echo "$@ is a dwarf planet"
|
||||||
|
@echo "dwarf is a type of planet"
|
||||||
|
@echo "therefore, $@ is a planet"
|
||||||
|
@echo "having lots of planets is good feature because supernovae can help ${MAKE} a lot of them"
|
||||||
+357
-310
@@ -1,351 +1,398 @@
|
|||||||
Best Utility:
|
# Best Utility:
|
||||||
|
|
||||||
Bernd Meyer
|
Bernd Meyer
|
||||||
Monash University, Melbourne, Australia
|
Monash University, Melbourne, Australia
|
||||||
1/832 Blackburn Rd
|
1/832 Blackburn Rd
|
||||||
Clayton, VIC 3168
|
Clayton, VIC 3168
|
||||||
Australia
|
Australia
|
||||||
|
|
||||||
http://byron.csse.monash.edu.au/
|
http://byron.csse.monash.edu.au/
|
||||||
|
|
||||||
|
# To build:
|
||||||
|
|
||||||
Judges' Comments:
|
```sh
|
||||||
|
make
|
||||||
|
```
|
||||||
|
|
||||||
To build:
|
### To run:
|
||||||
|
|
||||||
make bmeyer
|
```sh
|
||||||
|
./prog
|
||||||
|
```
|
||||||
|
|
||||||
Compile with the maximum possible optimization on your system.
|
### Try:
|
||||||
If your system has 80-bit internal representation of floating
|
|
||||||
point values (x86, some Motorola processors) and you want the
|
|
||||||
compressed format to be portable across platforms, you need
|
|
||||||
to set your FPU to use 64 bit mode. See the extra build lines
|
|
||||||
in the Makefile, and read the author's comments below.
|
|
||||||
|
|
||||||
If you cannot work out hwo to get into 64 bit mode, you can
|
In a video window (white text on black background):
|
||||||
try using -ffloat-store if you compile with GCC (this may have
|
|
||||||
a performance penalty). The resulting binary will have a good
|
|
||||||
chance to produce portable files, but due to the resulting
|
|
||||||
double-rounding (first internally to 80 bit, then to 64 bit
|
|
||||||
on writing the value to memory), there is a small but very real
|
|
||||||
chance any given file produced might not be portable.
|
|
||||||
|
|
||||||
To run:
|
```sh
|
||||||
|
./bmeyer < michael.pgm > michael.glic
|
||||||
|
```
|
||||||
|
|
||||||
In a video window (white text on black background):
|
Compare the michael.pgm to the screen output.
|
||||||
|
|
||||||
./bmeyer < michael.pgm > michael.glic
|
To test that you are compressing and decompressing the same way the
|
||||||
|
author was, try:
|
||||||
|
|
||||||
Compare the michael.pgm to the screen output.
|
```sh
|
||||||
|
./bmeyer < lenna.glic
|
||||||
|
```
|
||||||
|
|
||||||
To test that you are compressing and decompressing the same way the
|
Also try in a reverse video window:
|
||||||
author was, try
|
|
||||||
|
|
||||||
./bmeyer < lenna.glic
|
```sh
|
||||||
|
./bmeyer < michael.pgm 2>/dev/null | ./bmeyer > new.pgm
|
||||||
|
```
|
||||||
|
|
||||||
Also try in a reverse video window:
|
Compare the michael.pgm to the screen output. Compare the new.pgm file
|
||||||
|
to the michael.pgm file.
|
||||||
|
|
||||||
./bmeyer < michael.pgm 2>/dev/null | ./bmeyer > new.pgm
|
Create a large reverse video xterm, say 200 columns wide and try:
|
||||||
|
|
||||||
Compare the michael.pgm to the screen output. Compare the new.pgm file
|
```sh
|
||||||
to the michael.pgm file.
|
./bmeyer 200 < lavabus.pgm > lavabus.glic
|
||||||
|
```
|
||||||
|
|
||||||
Create a large reverse video xterm, say 200 columns wide and try:
|
Produce an even smaller output:
|
||||||
|
|
||||||
./bmeyer 200 < lavabus.pgm > lavabus.glic
|
```sh
|
||||||
|
./bmeyer -2 200 < lavabus.pgm > lavabus.glic2
|
||||||
|
```
|
||||||
|
|
||||||
Produce an even smaller output:
|
Decompress that smaller glic-file:
|
||||||
|
|
||||||
./bmeyer -2 200 < lavabus.pgm > lavabus.glic2
|
```sh
|
||||||
|
./bmeyer -2 200 < lavabus.glic2 > new.pgm
|
||||||
|
```
|
||||||
|
|
||||||
Decompress that smaller glic-file:
|
Compare the new.pgm file to the lavabus.pgm file by viewing them.
|
||||||
|
|
||||||
./bmeyer -2 200 < lavabus.glic2 > new.pgm
|
## Judges' comments:
|
||||||
|
|
||||||
Compare the new.pgm file to the lavabus.pgm file by viewing
|
Don't even think of supplying different compression factors (the
|
||||||
them.
|
dashed argument) for compression and decompression! You've been warned.
|
||||||
|
|
||||||
Don't even think of supplying different compression factors (the
|
The author recommended on linux/x86, glibc 2.0, libc4/5:
|
||||||
dashed argument) for compression and decompression! You've been warned.
|
|
||||||
|
|
||||||
|
```make
|
||||||
|
bmeyer: bmeyer.c
|
||||||
|
CC -DY="__setfpucw(0x127f)" -O6 $? -o $@ -lm
|
||||||
|
```
|
||||||
|
|
||||||
Selected Author's Comments:
|
However many compilers use -O3 as the maximum level for -O optimization.
|
||||||
|
|
||||||
GLICBAWLS
|
And on linux/x86, glibc 2.1:
|
||||||
|
|
||||||
A) Function
|
```make
|
||||||
===========
|
bmeyer: bmeyer.c
|
||||||
|
gcc -DY='int x=0x127f; __asm__ ("fldcw %0" : : "m" (*&x))' $? -o $@ -lm
|
||||||
|
```
|
||||||
|
|
||||||
"GLICBAWLS" stands for:
|
Compile with the maximum possible optimization on your system.
|
||||||
|
If your system has 80-bit internal representation of floating
|
||||||
|
point values (x86, some Motorola processors) and you want the
|
||||||
|
compressed format to be portable across platforms, you need
|
||||||
|
to set your FPU to use 64 bit mode. See the extra build lines
|
||||||
|
in the Makefile, and read the author's comments below.
|
||||||
|
|
||||||
"Grey Level Image Compression By Adaptive Weighted Least Squares".
|
If you cannot work out how to get into 64 bit mode, you can
|
||||||
|
try using -ffloat-store if you compile with GCC (this may have
|
||||||
|
a performance penalty). The resulting binary will have a good
|
||||||
|
chance to produce portable files, but due to the resulting
|
||||||
|
double-rounding (first internally to 80 bit, then to 64 bit
|
||||||
|
on writing the value to memory), there is a small but very real
|
||||||
|
chance any given file produced might not be portable.
|
||||||
|
|
||||||
And that's exactly what this program does --- feed it a .PGM file
|
The makefile defaults to -O3 and no `asm()` call.
|
||||||
(either raw [i.e. P5] or ascii [i.e. P2]) on stdin, and it will
|
|
||||||
output a compressed version to stdout. Feed it a compressed file
|
|
||||||
on stdin, and it will decompress it to stdout --- as either raw or
|
|
||||||
ascii .PGM, depending on what format it was compressed from. For
|
|
||||||
example:
|
|
||||||
|
|
||||||
./bmeyer < michael.pgm > michael.glic
|
## Author's comments:
|
||||||
|
|
||||||
and then
|
GLICBAWLS
|
||||||
|
|
||||||
./bmeyer < michael.glic > michael.decoded.pgm
|
A) Function
|
||||||
|
===========
|
||||||
|
|
||||||
As it turns out, glicbawls compresses greyscale images (or, more
|
"GLICBAWLS" stands for:
|
||||||
precisely, "natural" greyscale images) better than any other
|
|
||||||
program I am aware of (with the exception of the not-yet-published
|
|
||||||
program developed for my PhD thesis). Of course, this might take
|
|
||||||
some time, so a progress indicator is provided. To make things
|
|
||||||
more interesting, instead of a boring bar or percentage display,
|
|
||||||
an ASCII rendition of the image being compressed/decompressed is
|
|
||||||
output to stderr (assuming white text on black background). If you
|
|
||||||
have trouble recognizing the image, try squinting at it ;-).
|
|
||||||
|
|
||||||
If you still have trouble, simply use a terminal or xterm with
|
"Grey Level Image Compression By Adaptive Weighted Least Squares".
|
||||||
more than 80 columns, and tell glicbawls about it by giving the
|
|
||||||
number of columns as an argument. For example
|
|
||||||
|
|
||||||
./bmeyer 260 <lavabus.pgm >lavabus.glic
|
And that's exactly what this program does --- feed it a .PGM file
|
||||||
|
(either raw [i.e. P5] or ascii [i.e. P2]) on stdin, and it will
|
||||||
|
output a compressed version to stdout. Feed it a compressed file
|
||||||
|
on stdin, and it will decompress it to stdout --- as either raw or
|
||||||
|
ascii .PGM, depending on what format it was compressed from. For
|
||||||
|
example:
|
||||||
|
|
||||||
will allow glicbawls to use up to 260 columns, which makes things
|
```sh
|
||||||
much more recognizable.
|
./bmeyer < michael.pgm > michael.glic
|
||||||
|
```
|
||||||
|
|
||||||
Still running out of space? Need to compress those images just a
|
and then
|
||||||
tad more? And maybe you can handle some loss due to the
|
|
||||||
compression? If so, you can use glicbawls' "near lossless"
|
|
||||||
compression mode. In that mode, the decoded pixel values are
|
|
||||||
allowed to differ from tbe originals, but there is an upper limit
|
|
||||||
on the magnitude of the difference. For example, if a maximum
|
|
||||||
error of 2 is allowed, an original pixel value of 37 could be
|
|
||||||
decoded as 35,36,37, 38 or 39. In order to use this mode, simply
|
|
||||||
give the maximum allowed error as an argument, with a dash ('-')
|
|
||||||
before it. For example
|
|
||||||
|
|
||||||
./bmeyer -2 < graph.pgm > graph.2.glic
|
```sh
|
||||||
|
./bmeyer < michael.glic > michael.decoded.pgm
|
||||||
will compress in a way that allows decompression with a maximum
|
```
|
||||||
error of two. You can combine both types of arguments, i.e.
|
|
||||||
|
As it turns out, glicbawls compresses greyscale images (or, more
|
||||||
./bmeyer -3 180 < graph.pgm >graph.3.glic
|
precisely, "natural" greyscale images) better than any other
|
||||||
|
program I am aware of (with the exception of the not-yet-published
|
||||||
will compress with a maximum error of 3, using a 180 column
|
program developed for my PhD thesis). Of course, this might take
|
||||||
terminal for the progress display, and
|
some time, so a progress indicator is provided. To make things
|
||||||
|
more interesting, instead of a boring bar or percentage display,
|
||||||
./bmeyer -3 180 < graph.3.glic > graph.3maxerr.pgm
|
an ASCII rendition of the image being compressed/decompressed is
|
||||||
|
output to stderr (assuming white text on black background). If you
|
||||||
will decompress the result on such a terminal.
|
have trouble recognizing the image, try squinting at it ;-).
|
||||||
|
|
||||||
But wait, there is more --- you can also feed glicbawls .PPM files
|
If you still have trouble, simply use a terminal or xterm with
|
||||||
(i.e. colour images), raw or ascii, your choice. Glicbawls will
|
more than 80 columns, and tell glicbawls about it by giving the
|
||||||
compress and decompress them just fine. However, it only does
|
number of columns as an argument. For example
|
||||||
"reasonably well" on them; It beats PNG easily, but there are
|
|
||||||
certainly programs out there that can compress colour images
|
```sh
|
||||||
considerably better. And don't even *think* about using it for
|
./bmeyer 260 <lavabus.pgm >lavabus.glic
|
||||||
so-called "artistic" images (i.e. anything that wasn't scanned
|
```
|
||||||
from a photo or camera)....
|
|
||||||
|
will allow glicbawls to use up to 260 columns, which makes things
|
||||||
*****************************************************************
|
much more recognizable.
|
||||||
* *
|
|
||||||
* WARNING WARNING WARNING WARNING WARNING WARNING WARNING *
|
Still running out of space? Need to compress those images just a
|
||||||
* *
|
tad more? And maybe you can handle some loss due to the
|
||||||
* *
|
compression? If so, you can use glicbawls' "near lossless"
|
||||||
* Glicball is rather CPU and FPU intensive. Don't *
|
compression mode. In that mode, the decoded pixel values are
|
||||||
* run it on anything slow. Things start to be *
|
allowed to differ from tbe originals, but there is an upper limit
|
||||||
* usable around 300+MHz, with 600+ being highly *
|
on the magnitude of the difference. For example, if a maximum
|
||||||
* desirable. *
|
error of 2 is allowed, an original pixel value of 37 could be
|
||||||
* *
|
decoded as 35,36,37, 38 or 39. In order to use this mode, simply
|
||||||
*****************************************************************
|
give the maximum allowed error as an argument, with a dash ('-')
|
||||||
|
before it. For example
|
||||||
|
|
||||||
|
```sh
|
||||||
B) Compile Instructions
|
./bmeyer -2 < graph.pgm > graph.2.glic
|
||||||
=======================
|
```
|
||||||
|
|
||||||
Unlike most compression program, glicbawls makes heavy use of
|
will compress in a way that allows decompression with a maximum
|
||||||
floating point maths --- and not all FPUs are created equal. Most
|
error of two. You can combine both types of arguments, i.e.
|
||||||
importantly, the x86 and 68k FPUs use 80 bit floating point
|
|
||||||
formats internally, while most other processors use IEEE 64 bit
|
```sh
|
||||||
formats by default. If not taken care of, this means that a
|
./bmeyer -3 180 < graph.pgm >graph.3.glic
|
||||||
glicbawls file compressed on one CPU cannot generally be
|
```
|
||||||
decompressed on another.
|
|
||||||
|
will compress with a maximum error of 3, using a 180 column
|
||||||
Fortunately, just about all current FPUs can be put into IEEE 64
|
terminal for the progress display, and
|
||||||
bit mode (or at least something close enough for
|
|
||||||
glicbawls). Unfortunately, there is no standard way of doing
|
```sh
|
||||||
so. For this reason, the build file contains *three* compile
|
./bmeyer -3 180 < graph.3.glic > graph.3maxerr.pgm
|
||||||
lines; One for machines that already use 64 bit mode by default
|
```
|
||||||
(most RISC processors), one for linux/x86 machines using libc4,
|
|
||||||
libc5 or glibc2.0, and one for linux/x86 machines using glibc2.1
|
will decompress the result on such a terminal.
|
||||||
(glibc2.1 no longer exports the __setfpucw function, necessitating
|
|
||||||
the use of gcc inline assembly. *Grumble*).
|
But wait, there is more --- you can also feed glicbawls .PPM files
|
||||||
|
(i.e. colour images), raw or ascii, your choice. Glicbawls will
|
||||||
So, if you are building on a machine that does not, by default,
|
compress and decompress them just fine. However, it only does
|
||||||
use IEEE 64 bit floating point doubles, you'll have to define Y to
|
"reasonably well" on them; It beats PNG easily, but there are
|
||||||
be a command that switches it into that mode. If you fail to do
|
certainly programs out there that can compress colour images
|
||||||
so, your glicbawls executable will still be able to decompress its
|
considerably better. And don't even *think* about using it for
|
||||||
own compressed files, but you may be unable to exchange files with
|
so-called "artistic" images (i.e. anything that wasn't scanned
|
||||||
glicbawls on other machines.
|
from a photo or camera)....
|
||||||
|
|
||||||
|
*****************************************************************
|
||||||
C) Obfuscation
|
* *
|
||||||
==============
|
* WARNING WARNING WARNING WARNING WARNING WARNING WARNING *
|
||||||
|
* *
|
||||||
Most of the obfuscation of this program was driven by the
|
* *
|
||||||
desperate struggle to fit all of glicbawls' features into code
|
* Glicball is rather CPU and FPU intensive. Don't *
|
||||||
that fits the IOCCC's size limits. All identifiers names are
|
* run it on anything slow. Things start to be *
|
||||||
single-character, which was only possible by ruthless exploitation
|
* usable around 300+MHz, with 600+ being highly *
|
||||||
of scope. There is a function M() that handles nearly all input
|
* desirable. *
|
||||||
from stdin, handles all output to stdout, and also recursively
|
* *
|
||||||
calculates one of the mathematical expressions needed for error
|
*****************************************************************
|
||||||
modelling. There is a function that calculates (A^(-1)*b)*x with A
|
|
||||||
a matrix and b and x being vectors, and does so in a very
|
|
||||||
efficient way --- but one would be hard pressed to find it. There
|
|
||||||
is an arithmetic coder that is even less recognizable. A lot of
|
B) Compile Instructions
|
||||||
loop variables don't get initialized, but instead the code is
|
=======================
|
||||||
arranged in such a way that they just happen to have the right
|
|
||||||
value when control flow reaches the loops. Lots of functions use
|
Unlike most compression program, glicbawls makes heavy use of
|
||||||
the same two global scratch variables. Variables change their
|
floating point maths --- and not all FPUs are created equal. Most
|
||||||
meaning all the time, and the differences between compressing and
|
importantly, the x86 and 68k FPUs use 80 bit floating point
|
||||||
decompressing are handled in rather subtle ways all over the
|
formats internally, while most other processors use IEEE 64 bit
|
||||||
program. The string that holds the ascii values for displaying the
|
formats by default. If not taken care of, this means that a
|
||||||
progress image doubles as a description on how to find a pixel's
|
glicbawls file compressed on one CPU cannot generally be
|
||||||
causal neighbours. And then there are a few #define's that really
|
decompressed on another.
|
||||||
are just in there to save a few characters, but as an added
|
|
||||||
"benefit" make the source ever more unreadable.
|
Fortunately, just about all current FPUs can be put into IEEE 64
|
||||||
|
bit mode (or at least something close enough for
|
||||||
In short --- running it through the preprocessor and the
|
glicbawls). Unfortunately, there is no standard way of doing
|
||||||
pretty-printer will give you something that looks slightly less
|
so. For this reason, the build file contains *three* compile
|
||||||
like line noise and slightly more like a C program, but unless you
|
lines; One for machines that already use 64 bit mode by default
|
||||||
are a true wizard, it is unlikely to gain you any insights into
|
(most RISC processors), one for linux/x86 machines using libc4,
|
||||||
what is actually going on....[0]
|
libc5 or glibc2.0, and one for linux/x86 machines using glibc2.1
|
||||||
|
(glibc2.1 no longer exports the __setfpucw function, necessitating
|
||||||
|
the use of gcc inline assembly. *Grumble*).
|
||||||
D) Bugs, Assumptions and TODOs
|
|
||||||
==============================
|
So, if you are building on a machine that does not, by default,
|
||||||
|
use IEEE 64 bit floating point doubles, you'll have to define Y to
|
||||||
Glicbawls assumes that characters are 8 bit wide, and that the
|
be a command that switches it into that mode. If you fail to do
|
||||||
character set used is ASCII. If one of these isn't true, all hell
|
so, your glicbawls executable will still be able to decompress its
|
||||||
will break loose.
|
own compressed files, but you may be unable to exchange files with
|
||||||
|
glicbawls on other machines.
|
||||||
The .PGM headers are not checked very thoroughly --- glicbawls
|
|
||||||
will happily try to encode lots of files that it shouldn't
|
|
||||||
touch. The old adage of "garbage in, garbage out" holds in that
|
C) Obfuscation
|
||||||
case. Furthermore, even if glicbawls detects an incorrect input,
|
==============
|
||||||
it fails to provide a meaningful error message, and instead
|
|
||||||
simply aborts.
|
Most of the obfuscation of this program was driven by the
|
||||||
|
desperate struggle to fit all of glicbawls' features into code
|
||||||
When decompressing a near-losslessy encoded image, the maximum
|
that fits the IOCCC's size limits. All identifiers names are
|
||||||
allowed error is required as a command line parameter. This should
|
single-character, which was only possible by ruthless exploitation
|
||||||
really be saved in the compressed file!
|
of scope. There is a function M() that handles nearly all input
|
||||||
|
from stdin, handles all output to stdout, and also recursively
|
||||||
Glicbawls relies on the decimal representation of all integers
|
calculates one of the mathematical expressions needed for error
|
||||||
having less than 255 digits. While ANSI C does not guarantee this,
|
modelling. There is a function that calculates (A^(-1)*b)*x with A
|
||||||
it seems rather unlikely that anyone in the foreseeable future
|
a matrix and b and x being vectors, and does so in a very
|
||||||
would use images with 10^255 rows, columns or different levels of
|
efficient way --- but one would be hard pressed to find it. There
|
||||||
grey. Also, it is assumed that any integer used can be cast to a
|
is an arithmetic coder that is even less recognizable. A lot of
|
||||||
double and back without loss of precision. This limits the number
|
loop variables don't get initialized, but instead the code is
|
||||||
of rows, columns and grey levels to 9 quintillion, which should
|
arranged in such a way that they just happen to have the right
|
||||||
also be sufficient for the next few years.
|
value when control flow reaches the loops. Lots of functions use
|
||||||
|
the same two global scratch variables. Variables change their
|
||||||
There is a theoretical chance that you might get a division by
|
meaning all the time, and the differences between compressing and
|
||||||
zero error. You have a MUCH better chance of getting hit by
|
decompressing are handled in rather subtle ways all over the
|
||||||
lightning the very second you realize that you just won a few
|
program. The string that holds the ascii values for displaying the
|
||||||
million in a lottery. But if it happens to you, don't say I
|
progress image doubles as a description on how to find a pixel's
|
||||||
didn't warn you! Instead, go out and buy a lightning rod and a
|
causal neighbours. And then there are a few #define's that really
|
||||||
lottery ticket ;-)
|
are just in there to save a few characters, but as an added
|
||||||
|
"benefit" make the source ever more unreadable.
|
||||||
At one point, a pointer to int is used as the target of a "%1[#]"
|
|
||||||
conversion in a scanf, which makes gcc rather unhappy, but
|
In short --- running it through the preprocessor and the
|
||||||
shouldn't really cause anyone any trouble. The same goes for a
|
pretty-printer will give you something that looks slightly less
|
||||||
couple of assignments which are used as truth values.
|
like line noise and slightly more like a C program, but unless you
|
||||||
|
are a true wizard, it is unlikely to gain you any insights into
|
||||||
|
what is actually going on....[0]
|
||||||
E) Algorithm
|
|
||||||
============
|
|
||||||
|
D) Bugs, Assumptions and TODOs
|
||||||
An exhaustive explanation of the algorithm used would go beyond
|
==============================
|
||||||
the scope of an info file, and would also be quite difficult in
|
|
||||||
pure ASCII, so the following is just a rough outline, and contains
|
Glicbawls assumes that characters are 8 bit wide, and that the
|
||||||
some compression-speak...
|
character set used is ASCII. If one of these isn't true, all hell
|
||||||
|
will break loose.
|
||||||
The image is handled in scanline ordering. For each pixel, an
|
|
||||||
expected value is calculated by creating a least squares predictor
|
The .PGM headers are not checked very thoroughly --- glicbawls
|
||||||
of order 12 based on all of the previously encoded/decoded
|
will happily try to encode lots of files that it shouldn't
|
||||||
pixels. However, the contribution of each pixel is weighted
|
touch. The old adage of "garbage in, garbage out" holds in that
|
||||||
according to its Manhattan-distance from the current pixel,
|
case. Furthermore, even if glicbawls detects an incorrect input,
|
||||||
D. That weight used is pow(0.8,D). [1][2][3]
|
it fails to provide a meaningful error message, and instead
|
||||||
|
simply aborts.
|
||||||
|
|
||||||
In a similar way, the prediction *errors* for all previous pixels
|
When decompressing a near-losslessy encoded image, the maximum
|
||||||
are combined --- a weighted average (with weight pow(0.7,D)) of
|
allowed error is required as a command line parameter. This should
|
||||||
the squares of all previous prediction errors is taken, and the
|
really be saved in the compressed file!
|
||||||
square root of the (appropriately scaled) result is called sigma.
|
|
||||||
|
Glicbawls relies on the decimal representation of all integers
|
||||||
The predicted value and sigma are then used as the parameters of a
|
having less than 255 digits. While ANSI C does not guarantee this,
|
||||||
Student or t-distribution (which is similar to a normal
|
it seems rather unlikely that anyone in the foreseeable future
|
||||||
distribution, but has more weight in the tails), providing a
|
would use images with 10^255 rows, columns or different levels of
|
||||||
probability distribution for the current pixel.
|
grey. Also, it is assumed that any integer used can be cast to a
|
||||||
|
double and back without loss of precision. This limits the number
|
||||||
Next, the possible interval of values for the current pixel is
|
of rows, columns and grey levels to 9 quintillion, which should
|
||||||
halved, and through integration of the probability distribution, a
|
also be sufficient for the next few years.
|
||||||
probability is calculated for the pixel value being in the lower
|
|
||||||
half. During encoding, the actual value is examined, and the
|
There is a theoretical chance that you might get a division by
|
||||||
result encoded using an arithmetic coder. During decoding, the
|
zero error. You have a MUCH better chance of getting hit by
|
||||||
arithmetic decoder provides the information which half the actual
|
lightning the very second you realize that you just won a few
|
||||||
value is in. In both cases, the interval borders are adjusted
|
million in a lottery. But if it happens to you, don't say I
|
||||||
accordingly, the arithmetic coder/decoder updated, and the
|
didn't warn you! Instead, go out and buy a lightning rod and a
|
||||||
interval halving repeated until the precise value has been
|
lottery ticket ;-)
|
||||||
en/decoded[4].
|
|
||||||
|
At one point, a pointer to int is used as the target of a "%1[#]"
|
||||||
|
conversion in a scanf, which makes gcc rather unhappy, but
|
||||||
[0] Yes, this could be seen as a challenge....
|
shouldn't really cause anyone any trouble. The same goes for a
|
||||||
[1] Actually, the weight is pow(0.8,D)/s, where s is the sigma
|
couple of assignments which are used as truth values.
|
||||||
used for en/decoding the particular previous pixel. Dividing
|
|
||||||
by s is a rather arbitrary action justified only by the
|
|
||||||
improvement in results. Mathematically, I can only justify
|
E) Algorithm
|
||||||
dividing by s^2, or not dividing at all....
|
============
|
||||||
[2] Obviously, these least squares predictors are not calculated
|
|
||||||
from scratch for each pixel. Some clever reuse of earlier
|
An exhaustive explanation of the algorithm used would go beyond
|
||||||
results allows O(1) calculation, rather than the
|
the scope of an info file, and would also be quite difficult in
|
||||||
O(previous_rows*columns) this description would suggest.
|
pure ASCII, so the following is just a rough outline, and contains
|
||||||
[3] As anyone who has ever tried local least squares knows from
|
some compression-speak...
|
||||||
bitter experience, there is a lot of numerical instability
|
|
||||||
associated with them. So glicbawls adds a bias towards an
|
The image is handled in scanline ordering. For each pixel, an
|
||||||
averaging predictor to the equation system the least squares
|
expected value is calculated by creating a least squares predictor
|
||||||
predictor is calculated from. The weight that is given to
|
of order 12 based on all of the previously encoded/decoded
|
||||||
this bias is constantly adjusted throughout coding/decoding,
|
pixels. However, the contribution of each pixel is weighted
|
||||||
thus justifying the 'a' in "glicbawls".
|
according to its Manhattan-distance from the current pixel,
|
||||||
[4] In the case of near-lossless coding, the interval is not
|
D. That weight used is pow(0.8,D). [1][2][3]
|
||||||
necessarily *halved*, but rather split at a convenient point
|
|
||||||
(the split points are chosen in such a way as to minimise the
|
|
||||||
expected number of bits needed for coding). Also, the
|
In a similar way, the prediction *errors* for all previous pixels
|
||||||
iteration ends as soon as the interval is small enough to
|
are combined --- a weighted average (with weight pow(0.7,D)) of
|
||||||
guarantee decoding within the requested maximum error.
|
the squares of all previous prediction errors is taken, and the
|
||||||
|
square root of the (appropriately scaled) result is called sigma.
|
||||||
####################################################################
|
|
||||||
|
The predicted value and sigma are then used as the parameters of a
|
||||||
Photo Credit:
|
Student or t-distribution (which is similar to a normal
|
||||||
|
distribution, but has more weight in the tails), providing a
|
||||||
Lavabus was taken by the judge, Landon Curt Noll. Michael was
|
probability distribution for the current pixel.
|
||||||
provided by the author. Lenna is a 1972 Playboy centerfold.
|
|
||||||
|
Next, the possible interval of values for the current pixel is
|
||||||
michael.pgm
|
halved, and through integration of the probability distribution, a
|
||||||
|
probability is calculated for the pixel value being in the lower
|
||||||
The author's Godchild and nephew.
|
half. During encoding, the actual value is examined, and the
|
||||||
|
result encoded using an arithmetic coder. During decoding, the
|
||||||
lavabus.pgm
|
arithmetic decoder provides the information which half the actual
|
||||||
|
value is in. In both cases, the interval borders are adjusted
|
||||||
A bus that was trapped by lava from Kilauea volcano in
|
accordingly, the arithmetic coder/decoder updated, and the
|
||||||
Hawaii, USA. Nobody was in the bus at the time, BTW.
|
interval halving repeated until the precise value has been
|
||||||
Photo date: 1981.
|
en/decoded[4].
|
||||||
|
|
||||||
lenna.glic
|
|
||||||
|
[0] Yes, this could be seen as a challenge....
|
||||||
A November 1972 Playboy centerfold was scanned in long ago and
|
[1] Actually, the weight is pow(0.8,D)/s, where s is the sigma
|
||||||
has been used for image compression research since then. Playboy
|
used for en/decoding the particular previous pixel. Dividing
|
||||||
originally threatened to prosecute unauthorized use, but
|
by s is a rather arbitrary action justified only by the
|
||||||
eventually granted that, having been in use for image compression
|
improvement in results. Mathematically, I can only justify
|
||||||
testing for so long, it was now a useful benchmark. (Note: This
|
dividing by s^2, or not dividing at all....
|
||||||
picture doesn't show very much.)
|
[2] Obviously, these least squares predictors are not calculated
|
||||||
|
from scratch for each pixel. Some clever reuse of earlier
|
||||||
|
results allows O(1) calculation, rather than the
|
||||||
|
O(previous_rows*columns) this description would suggest.
|
||||||
|
[3] As anyone who has ever tried local least squares knows from
|
||||||
|
bitter experience, there is a lot of numerical instability
|
||||||
|
associated with them. So glicbawls adds a bias towards an
|
||||||
|
averaging predictor to the equation system the least squares
|
||||||
|
predictor is calculated from. The weight that is given to
|
||||||
|
this bias is constantly adjusted throughout coding/decoding,
|
||||||
|
thus justifying the 'a' in "glicbawls".
|
||||||
|
[4] In the case of near-lossless coding, the interval is not
|
||||||
|
necessarily *halved*, but rather split at a convenient point
|
||||||
|
(the split points are chosen in such a way as to minimise the
|
||||||
|
expected number of bits needed for coding). Also, the
|
||||||
|
iteration ends as soon as the interval is small enough to
|
||||||
|
guarantee decoding within the requested maximum error.
|
||||||
|
|
||||||
|
####################################################################
|
||||||
|
|
||||||
|
Photo Credit:
|
||||||
|
|
||||||
|
Lavabus was taken by the judge, Landon Curt Noll. Michael was
|
||||||
|
provided by the author. Lenna is a 1972 Playboy centerfold.
|
||||||
|
|
||||||
|
michael.pgm
|
||||||
|
|
||||||
|
The author's Godchild and nephew.
|
||||||
|
|
||||||
|
lavabus.pgm
|
||||||
|
|
||||||
|
A bus that was trapped by lava from Kilauea volcano in
|
||||||
|
Hawaii, USA. Nobody was in the bus at the time, BTW.
|
||||||
|
Photo date: 1981.
|
||||||
|
|
||||||
|
lenna.glic
|
||||||
|
|
||||||
|
A November 1972 Playboy centerfold was scanned in long ago and
|
||||||
|
has been used for image compression research since then. Playboy
|
||||||
|
originally threatened to prosecute unauthorized use, but
|
||||||
|
eventually granted that, having been in use for image compression
|
||||||
|
testing for so long, it was now a useful benchmark. (Note: This
|
||||||
|
picture doesn't show very much.)
|
||||||
Reference in new issue
Block a user