Landon Curt Noll
c457b16358
Renamed `ioccc.ico` to `favicon.ico`. Correctly added use of `favicon.ico` to all constructed HTML headers. Fixed the smart quote in HTML elements problem. Moved HTML "DO NOT EDIT" comments down below at the bottom of the HTML phase 1 section. According to to the Nu Html Checker, a charset attribute on a meta element found after the first 1024 bytes. Changed `bin/md2html.sh` VERSION from "1.1.3 2024-03-28" to "1.2 2024-03-30". Improved `bin/gen-status.sh` to adjust the "status_update" value only when the "contest_status" is changed. Performed a `make www` to perform and test the above under macOS.
To build:
make all
To use:
./dds basic_program
./a.out 2>/dev/null
Try:
The author suggests trying:
./dds LANDER.BAS
./a.out
Notice that a file a.c has been generated. Can you tell how a.c was
produced? How does a.c relate to LANDER.BAS?
What happens if you give the program a C program like itself? Try:
./dds dds.c
You'll get errors yes but what does the generated file look like? What about other types of files?
Judges' remarks:
This obfuscated program translates BASIC programs into obfuscated C programs by way of an obfuscated algorithm.
Author's remarks:
This program is a companion to the 1990/dds
1990 DDS-BASIC interpreter program. This compiles BASIC programs into compilable C code
and then compiles it. The input format is almost identical to the input format
of the DDS-BASIC interpreter. The program needs an executable C compiler called
cc in your path in order to work.
Program commands:
- variable names
AtoZ - FOR var = exp TO exp
- GOSUB exp
- GOTO exp
- INPUT variable
- PRINT exp
- REM any text
- variables initialized to 0 on RUN
- NEXT variable
- RETURN
- IF exp THEN exp
- PRINT string
- var = exp
- END
Expressions are the same as the expressions of the C language. Many system calls and C library calls can be used.
Input format:
- Free format positioning of tokens on the line.
- No space is allowed before the line number.
- Exactly one space is needed after the
FORandNEXTtokens. - ALL INPUT MUST BE UPPERCASE.
Error checking / error reports:
The compiler silently ignores many errors. Other errors may produce errors in later phases of the compilation.
Can you figure out how the compiler works?
Hint:
The compiler is NOT written in C, so this is really a meta-obfuscated
program. The C code is an interpreter for the four register, seven
instruction COGNIMP$ machine that is contained in the s string.
(COGNIMP$ is named after the symbolic names of the seven instructions it
defines (Copy, Output, Goto, iNcrement, If, Match and Print).
The $ sign is used for labels. The actual compiler is written in COGNIMP$.
Browsing through the COGNIMP$ code we encourage you to examine the loops for
scanning the expression in the IF statement and the way a decision tree is
implemented in order to match the statements. (Of course the s string is
encoded by adding one to every character of it just to confuse you).