Cody Boone Ferguson
3fdb24beb9
In 1991 the code blocks in the html files should look better with smaller screens. In one entry, rince, an image was added as the formatting is too complicated to get right. The text was changed from two columns to one column and then a screenshot was taken so that it's a bit easier to see with smaller widths. This looks fairly good on mobile phones too. The only downside, of course, is if the web pages ever change to have a different background or code colour it won't match but it did not look right with mobile phones. This required a manifest update. In 1992 one entry's html file defeated me for now so I had to stop. This can be looked at later. The last entry I am committing changes to is 1991/buzzard.1. It was buzzard.2/buzzard.2.design.md that is a big problem and will have to be done another time.
116 lines
2.9 KiB
Markdown
116 lines
2.9 KiB
Markdown
## To build:
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``` <!---sh-->
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make all
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```
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## To use:
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``` <!---sh-->
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./dds basic_program
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./a.out 2>/dev/null
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```
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## Try:
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The author suggests trying:
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``` <!---sh-->
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./dds LANDER.BAS
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./a.out
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```
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Notice that a file `a.c` has been generated. Can you tell how `a.c` was
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produced? How does `a.c` relate to [LANDER.BAS](%%REPO_URL%%/1991/dds/LANDER.BAS)?
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What happens if you give the program a C program like itself? Try:
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``` <!---sh-->
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./dds dds.c
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```
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You'll get errors yes but what does the generated file look like? What about
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other types of files?
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## Judges' remarks:
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This obfuscated program translates BASIC programs into obfuscated
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C programs by way of an obfuscated algorithm.
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## Author's remarks:
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This program is a companion to the [1990/dds](../../1990/dds/index.html)
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1990 DDS-BASIC interpreter program. This compiles BASIC programs into compilable C code
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and then compiles it. The input format is almost identical to the input format
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of the DDS-BASIC interpreter. The program needs an executable C compiler called
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`cc` in your path in order to work.
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### Program commands:
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- variable names A to Z
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- FOR var = exp TO exp
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- GOSUB exp
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- GOTO exp
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- INPUT variable
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- PRINT exp
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- REM any text
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- variables initialized to 0 on RUN
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- NEXT variable
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- RETURN
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- IF exp THEN exp
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- PRINT string
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- var = exp
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- END
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Expressions are the same as the expressions of the C language.
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Many system calls and C library calls can be used.
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### Input format:
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- Free format positioning of tokens on the line.
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- No space is allowed before the line number.
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- Exactly one space is needed after the `FOR` and `NEXT` tokens.
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- ALL INPUT MUST BE UPPERCASE.
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### Error checking / error reports:
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The compiler silently ignores many errors.
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Other errors may produce errors in later phases of the compilation.
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### Can you figure out how the compiler works?
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#### Hint:
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The compiler is NOT written in C, so this is really a meta-obfuscated
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program. The C code is an interpreter for the four register, seven
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instruction `COGNIMP$` machine that is contained in the `s` string.
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(`COGNIMP$` is named after the symbolic names of the seven instructions it
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defines (`Copy`, `Output`, `Goto`, `iNcrement`, `If`, `Match` and `Print`).
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The `$` sign is used for labels. The actual compiler is written in `COGNIMP$`.
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Browsing through the `COGNIMP$` code we encourage you to examine the loops for
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scanning the expression in the `IF` statement and the way a decision tree is
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implemented in order to match the statements. (Of course the `s` string is
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encoded by adding one to every character of it just to confuse you).
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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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