Fix formatting and link in 1998/schweikh2
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Cody Boone Ferguson committed
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@@ -1,17 +1,18 @@
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# Most Erratic Behavior
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Jens Schweikhardt
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DFN Network Operation Center
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Schlartaeckerweg 3 (Home address)
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D-71384 Weinstadt
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Germany
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http://www.shuttle.de/schweikh/
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Jens Schweikhardt
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DFN Network Operation Center
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Schlartaeckerweg 3 (Home address)
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D-71384 Weinstadt
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Germany
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<http://www.schweikhardt.net>
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## To build:
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make all
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```sh
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make all
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```
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NOTE: Almost every compiler is supposed to be able to accept the code in
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`schweikh2.c`; try compiling `schweikh2.alt.c` to see if your compiler
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@@ -19,29 +20,36 @@ is fully standard-compliant.
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## To run:
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To use:
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./schweikh2
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<some number>
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```sh
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./schweikh2
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<some number>
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```
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or
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./schweikh2 integer_number
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```sh
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./schweikh2 integer_number
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```
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## Try:
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./schweikh2 5
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./schweikh2 5
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```sh
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./schweikh2 5
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./schweikh2 5
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./schweikh2
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5
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./schweikh2
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5
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```
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What is the difference here?
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What happens if you don't put in any number like the below?
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./schweikh2
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<ENTER>
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```sh
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./schweikh2
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<ENTER>
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```
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## Judges' remarks:
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@@ -55,39 +63,52 @@ entry correctly.
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At the time this hint file was written, some gcc and egcs implementations ran
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into problem when building the original entry:
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make schweikh2.alt
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```sh
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make schweikh2.alt
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```
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This program often will produce an error of the form:
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gcc -ansi schweikh2.alt.c -o schweikh2.alt
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as: Error: cca00NzV.s, line 58: Missing " at end of string
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"
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as: Error: cca00NzV.s, line 58: malformed statement
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*** Error code 1 (bu21)
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```
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gcc -ansi schweikh2.alt.c -o schweikh2.alt
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as: Error: cca00NzV.s, line 58: Missing " at end of string
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"
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as: Error: cca00NzV.s, line 58: malformed statement
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*** Error code 1 (bu21)
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```
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because the line:
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??=line 10 ONE(O(1,1,2,6,0,6))
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```c
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??=line 10 ONE(O(1,1,2,6,0,6))
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```
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turns into the line:
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# 9 "01\012"
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```c
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# 9 "01\012"
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```
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which causes gcc to give to the assembler the following two lines:
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.stabs "whey.c
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",132,0,0,Ltext1
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```asm
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.stabs "whey.c
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",132,0,0,Ltext1
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```
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and the lone " after the #.file line results in an assembler syntax error.
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and the lone `"` after the `#.file` line results in an assembler syntax error.
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In some cases one must compile using `gcc -g`:
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make schweikh2.alt CFLAGS=-g
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```sh
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make schweikh2.alt CFLAGS=-g
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```
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to trigger this error.
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And with the proper text beyond the `\012`, it may be possible to have
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all kinds of fun adding `inline assembly` via #line directives. :-)
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all kinds of fun adding `inline assembly` via `#line` directives. :-)
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For extra credit:
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If your compiler has this bug, transform the line in the C
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@@ -97,18 +118,17 @@ the program will compile.
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If you are able to do the above, try adding assembly instructions
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so that it will compile, execute and do something interesting.
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If you succeed in doing this (especially on FreeBSD, Linux or Sparc),
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If you succeed in doing this (especially on FreeBSD, Linux or SPARC),
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email the author for a free pat on the back.
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NOTE: the author submitted the program as yarng so when trying the examples
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NOTE: the author submitted the program as `yarng` so when trying the examples
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below change `yarng` to `./schweikh2`.
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## Author's remarks:
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What this program does
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----------------------
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### What this program does
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My entry is a yarng, which stands for, you guessed it, yet another
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My entry is a `yarng`, which stands for, you guessed it, yet another
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random number generator, and is pronounced 'yawn' due to its
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incredible speed. Seriously, it exploits the randomness of quantum
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mechanical events that build up the hardware as well as some other
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@@ -120,7 +140,7 @@ non-deterministic factors. Here's how it works:
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4. while some other counter is not zero, go to 1)
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5. exit
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The yarng therefore produces output at a rate of 1 baud. The number of
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The `yarng` therefore produces output at a rate of 1 baud. The number of
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bits may be specified by an argument and defaults either to `UINT_MAX`
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(least likely) or `UINT_MAX+1` (most likely). Extra credit: why the
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different values? How long would you need for an empirical test?
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@@ -128,19 +148,18 @@ different values? How long would you need for an empirical test?
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For example:
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```sh
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$ yarng 32
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$ ./yarng 32
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10111001010101110110010101001111
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$ yarng 5
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$ ./yarng 5
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10011
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```
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Why I think this is obfuscated
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------------------------------
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### Why I think this is obfuscated
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- Ever seen a 'do for ... while' loop?
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- I avoided 'int' like the plague. Instead I used storage class specifiers
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(register, auto) to get implicit int. The Standard allows implicit int even in
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- I avoided `int` like the plague. Instead I used storage class specifiers
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(`register`, `auto`) to get implicit int. The Standard allows implicit int even in
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casts as you can see in `(void(*)(register))main`. Where implicit int is
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impossible, like in the `int main` declaration I have int split across two
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lines. All indent programs I use insert space at the beginning of the
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@@ -148,7 +167,7 @@ continuation line and thereby introduce a syntax error.
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- `main` (ab)used as a signal handler. Shocking. Yeah, this leads to undefined
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behaviour. I have yet to see a system where it does not work. If it doesn't work
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for you, I'd appreciate if you mail me about it. Uh-oh, schweikh did it,
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for you, I'd appreciate if you mail me about it. Uh-oh, Schweikh did it,
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uttered "Works for me". Don't quote me on that!
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- Even if you know how the program works, you just can't predict the output.
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@@ -159,7 +178,7 @@ uttered "Works for me". Don't quote me on that!
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preprocessor directive does the trick. But saying `#line 10 "01\n"` is a little
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lame and I came up with `??=line 10 ONE(O(1,1,2,6,0,6))`.
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- `__LINE__` is used as the signal number argument to signal(). If indenting or
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- `__LINE__` is used as the signal number argument to `signal()`. If indenting or
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other editing changes the number of lines the program is likely to be killed
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after one second... Thanks to POSIX for specifying SIGALRM as 14. You're SOL if
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your system does not conform. Get a real OS.
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@@ -175,7 +194,7 @@ this line and prepare for a core dump.
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and as a plain identifier in `main`'s parameters. The rule is that whenever
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`ONE` is followed by `(` it must be the macro.
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- A quote from Kernighan and Plauger, "The Elements of Programming Style", 2nd
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- A quote from Kernighan and Plauger, _The Elements of Programming Style_, 2nd
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Ed., page 21: "A useful way to decide if some piece of code is clear or not is
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the 'telephone test.' If someone could understand your code when read aloud
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over the telephone, it's clear enough. If not then it needs rewriting." Now try
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@@ -184,8 +203,7 @@ the telephone test for 'one = zero = atoi (ONE[zero-1])'.
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- Don't you love the aesthetics of symmetry: `write (1, 1+__FILE__+1, 1)`
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(telephone test this as well; is it 1, One, ONE, one? Maybe won?).
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Where does the randomness come from?
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------------------------------------
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### Where does the randomness come from?
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Each bit obviously depends on the number of times the loop body is
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executed between two calls of the signal handler. But what determines
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@@ -196,24 +214,24 @@ this number?
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- On multitasking OS's: The total time the process is scheduled to run between
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successive invocations of the signal handler.
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How about the randomness of the yarng? To measure these properties I
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How about the randomness of the `yarng`? To measure these properties I
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counted the number of bit sequences and compared them to what I would
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expect from a generator with uniform distribution (all sequences
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equally likely to occur).
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It is interesting to note that yarng's maximum deviations are less
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than or equal to rand()'s. Randomness however tends to degrade under
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It is interesting to note that `yarng`'s maximum deviations are less
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than or equal to `rand()`'s. Randomness however tends to degrade under
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high load averages on my system (Linux). This could be avoided by
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allowing the process one second of execution time instead of wall
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clock time (using the `SIGVTALRM` sent by the virtual timer
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instead of `SIGALRM`).
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I'm not surprised. Yarng in the end depends on fluctuations of the
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I'm not surprised. `Yarng` in the end depends on fluctuations of the
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electrical field and the heat distribution in the oscillators, the
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implementation and state of the scheduling algorithm, the system
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load, number and temporal distribution of asynchronous events and
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last but not least the phase of the moon. God _does_ play dice.
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Type yarng and watch Him roll.
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Type `yarng` and watch Him roll.
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## Copyright and CC BY-SA 4.0 License:
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