Cody Boone Ferguson
22e483723c
Instead of code blocks the bug / (mis)features statuses are quoted rather than in a code block. In the case that there is more than one a line break was added at the end of all but the last one. A bug status was renamed to be slightly more correct (maybe more than one was renamed for the same purpose but at least one was). The bug statuses in the quotes are now bold to let them stand out better.
137 lines
3.1 KiB
Markdown
137 lines
3.1 KiB
Markdown
## To build:
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``` <!---sh-->
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make
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```
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### Bugs and (Mis)features:
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The current status of this entry is:
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> **STATUS: INABIAF - please DO NOT fix**
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For more detailed information see [2020/burton in bugs.html](../../bugs.html#2020_burton).
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## To use:
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``` <!---sh-->
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./prog arg ...
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```
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## Try:
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``` <!---sh-->
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./try.sh
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```
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## Alternate code:
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By default, the program works for Little Endian machines. This alternate build
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is for Big Endian machines (that works whether you have LE or BE).
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### Alternate build:
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Running `make` builds the alternate code by default.
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### Alternate use:
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Use `prog_be` as you would `prog` above.
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## Judges' remarks:
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Can you determine why this shows strange output for `./prog 128 128`
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and `./prog 128 128 128 128` but not `./prog 128 128 128`?
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Can you find a pattern here?
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What happens if you specify different numbers?
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This tiny one-liner is a bit-twiddler's delight! It does all of the work
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without looping.
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To understand how it works, a good place to start is to look at the hex
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value that results when the two magic constants are `XOR`ed.
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Once you've figured out what happens with one set of constants, how can
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choosing new constants, but using the same computation generate a reversed
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result?
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This code may be tested by:
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``` <!---sh-->
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make test
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```
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## Author's remarks:
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Invoke this with a single non-negative integer less than 256, and a useful
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transformation occurs.
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### Rule 2-ish:
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Exporting the constants `B`,`I`,`T`,`S` to the [Makefile](%%REPO_URL%%/2020/burton/Makefile) allows the
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code to be compiled for either LE (little-endian) or BE (big-endian)
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machines(!!), so they are truly configuration parameters, not logic.
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### Notes:
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One <del>ping</del> argument only. It will segfault on zero arguments, and
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display strange results with more than one argument.
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Small, non-negative integers only. Useful range is `0 .. 511`, sorta, for LE; `0
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.. 255` for BE. Bonus points if you can explain why the limits work this way.
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ASCII character set, 64-bit `long long`s are required.
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v,a,r,i,a,b,l,e,s\_NAME the operation.
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No loops, no branches?!?
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#### Compilation:
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Compiles cleanly under `clang -Wall -Weverything -pedantic`, but you need to add
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`--include stdio.h --include stdlib.h` for the `printf(3)` and `atoi(3)`.
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On a little-endian machine:
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``` <!---sh-->
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clang -include stdio.h -include stdlib.h -Wall -Weverything -pedantic -DB=6945503773712347754LL -DI=5859838231191962459LL -DT=0 -DS=7 -o prog prog.c
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```
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On a big-endian machine:
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``` <!---sh-->
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clang -include stdio.h -include stdlib.h -Wall -Weverything -pedantic -DB=7091606191627001958LL -DI=6006468689561538903LL -DT=1 -DS=0 -o prog_be prog.c
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```
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You might be interested to compile it both ways on the same host, and try:
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``` <!---sh-->
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./prog 1; ./prog_be 1
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```
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<!--
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Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.
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You are free to share and adapt this file under the terms of this license:
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Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
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For more information, see:
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https://creativecommons.org/licenses/by-sa/4.0/
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-->
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