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Fix 2015/endoh3/README.md

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Fix dead link. Apout is no longer available at the location in the
README.md. Instead it's on GitHub. I checked it and it's the same
author, Warren Toomey of TUHS so I know it's good (or at least the
program is: not sure if the repo is owned by him).

Format fixes.

Fix ioccc.org link (though it shouldn't be necessary since mullender.c
is actually in the repo).
This commit is contained in:
Cody Boone Ferguson committed 2023-03-25 11:34:43 -07:00
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@@ -26,31 +26,36 @@ make -B BACK_TO=ioccc.c
## Judges' comments:
Like Marty and Doc, something nostalgic from 1984 appears live in October of 2015!
Like Marty and Doc, something nostalgic from 1984 appears live in October of
2015!
The author of this gem is a true Delorean!
A question for inquisitive readers: is the implemented subset of PDP-11 instructions Turing-complete?
(For a clue, see the end of the author's remarks.)
If in doubt, use [APOUT](http://www.tuhs.org/Archive/PDP-11/Emulators/Apout/).
A question for inquisitive readers: is the implemented subset of PDP-11
instructions Turing-complete? (For a clue, see the end of the author's remarks.)
If in doubt, use [APOUT](https://github.com/DoctorWkt/Apout).
## Author's comments:
### Hint / Compatibility
* A little-endian system is required due to an external factor.
* Strictly speaking, this program does not comply with any C specification for the same reason. But I believe it is reasonably portable.
* Strictly speaking, this program does not comply with any C specification for
the same reason. But I believe it is reasonably portable.
* It uses a GCC extension but works on clang.
* This is a kind of emulator. You may find its architecture name if you look at the source code from all angles.
* This is a kind of emulator. You may find its architecture name if you look at
the source code from all angles..
* Find main() function.
### Spoiler
This program is a joke PDP-11 emulator. ("ll-dpd" is embedded in the code. Read it upside down.)
This program is a joke PDP-11 emulator. ("ll-dpd" is embedded in the code.
Read it upside down.)
You got it? This program is supposed to be used in this way:
```sh
wget http://ioccc.org/1984/mullender.c
wget https://www.ioccc.org/1984/mullender.c
clang -o prog prog.c mullender.c
./prog
```
@@ -59,9 +64,12 @@ You can enjoy the legendary winner of the first IOCCC, again.
### Internal
This program uses `__attribute__((constructor))`, which is a GCC extension, to hijack the main function call. And then it interprets main as an instruction sequence.
This program uses `__attribute__((constructor))`, which is a GCC extension, to
hijack the main function call. And then it interprets main as an instruction
sequence.
It supports the minimal subset of instructions and addressing modes which are needed for mullender.c to work:
It supports the minimal subset of instructions and addressing modes which are
needed for mullender.c to work:
* Instructions
* BR: branch
@@ -80,7 +88,10 @@ It supports the minimal subset of instructions and addressing modes which are ne
### Limitation
Non-trivial combination of instruction and addressing mode may cause undefined behavior (unsequenced modification), such as attempting to autoincrement a destination register. Index addressing mode works well only for R7 (PC register).
Non-trivial combination of instruction and addressing mode may cause undefined
behavior (unsequenced modification), such as attempting to autoincrement a
destination register. Index addressing mode works well only for R7 (PC
register).
### One more thing