diff --git a/1998/schweikh2/README.md b/1998/schweikh2/README.md index e2cc7988e..4e9781b72 100644 --- a/1998/schweikh2/README.md +++ b/1998/schweikh2/README.md @@ -1,17 +1,18 @@ # Most Erratic Behavior - Jens Schweikhardt - DFN Network Operation Center - Schlartaeckerweg 3 (Home address) - D-71384 Weinstadt - Germany - - http://www.shuttle.de/schweikh/ +Jens Schweikhardt +DFN Network Operation Center +Schlartaeckerweg 3 (Home address) +D-71384 Weinstadt +Germany + ## To build: - make all +```sh +make all +``` NOTE: Almost every compiler is supposed to be able to accept the code in `schweikh2.c`; try compiling `schweikh2.alt.c` to see if your compiler @@ -19,29 +20,36 @@ is fully standard-compliant. ## To run: -To use: - ./schweikh2 - +```sh +./schweikh2 + +``` or - ./schweikh2 integer_number +```sh +./schweikh2 integer_number +``` ## Try: - ./schweikh2 5 - ./schweikh2 5 +```sh +./schweikh2 5 +./schweikh2 5 - ./schweikh2 - 5 +./schweikh2 +5 +``` What is the difference here? What happens if you don't put in any number like the below? - ./schweikh2 - +```sh +./schweikh2 + +``` ## Judges' remarks: @@ -55,39 +63,52 @@ entry correctly. At the time this hint file was written, some gcc and egcs implementations ran into problem when building the original entry: - make schweikh2.alt +```sh +make schweikh2.alt +``` This program often will produce an error of the form: - gcc -ansi schweikh2.alt.c -o schweikh2.alt - as: Error: cca00NzV.s, line 58: Missing " at end of string - " - as: Error: cca00NzV.s, line 58: malformed statement - *** Error code 1 (bu21) +``` +gcc -ansi schweikh2.alt.c -o schweikh2.alt +as: Error: cca00NzV.s, line 58: Missing " at end of string + " +as: Error: cca00NzV.s, line 58: malformed statement +*** Error code 1 (bu21) +``` because the line: - ??=line 10 ONE(O(1,1,2,6,0,6)) +```c +??=line 10 ONE(O(1,1,2,6,0,6)) +``` turns into the line: - # 9 "01\012" +```c +# 9 "01\012" + +``` which causes gcc to give to the assembler the following two lines: - .stabs "whey.c - ",132,0,0,Ltext1 +```asm +.stabs "whey.c +",132,0,0,Ltext1 +``` -and the lone " after the #.file line results in an assembler syntax error. +and the lone `"` after the `#.file` line results in an assembler syntax error. In some cases one must compile using `gcc -g`: - make schweikh2.alt CFLAGS=-g +```sh +make schweikh2.alt CFLAGS=-g +``` to trigger this error. And with the proper text beyond the `\012`, it may be possible to have -all kinds of fun adding `inline assembly` via #line directives. :-) +all kinds of fun adding `inline assembly` via `#line` directives. :-) For extra credit: If your compiler has this bug, transform the line in the C @@ -97,18 +118,17 @@ the program will compile. If you are able to do the above, try adding assembly instructions so that it will compile, execute and do something interesting. -If you succeed in doing this (especially on FreeBSD, Linux or Sparc), +If you succeed in doing this (especially on FreeBSD, Linux or SPARC), email the author for a free pat on the back. -NOTE: the author submitted the program as yarng so when trying the examples +NOTE: the author submitted the program as `yarng` so when trying the examples below change `yarng` to `./schweikh2`. ## Author's remarks: -What this program does ----------------------- +### What this program does -My entry is a yarng, which stands for, you guessed it, yet another +My entry is a `yarng`, which stands for, you guessed it, yet another random number generator, and is pronounced 'yawn' due to its incredible speed. Seriously, it exploits the randomness of quantum mechanical events that build up the hardware as well as some other @@ -120,7 +140,7 @@ non-deterministic factors. Here's how it works: 4. while some other counter is not zero, go to 1) 5. exit -The yarng therefore produces output at a rate of 1 baud. The number of +The `yarng` therefore produces output at a rate of 1 baud. The number of bits may be specified by an argument and defaults either to `UINT_MAX` (least likely) or `UINT_MAX+1` (most likely). Extra credit: why the different values? How long would you need for an empirical test? @@ -128,19 +148,18 @@ different values? How long would you need for an empirical test? For example: ```sh -$ yarng 32 +$ ./yarng 32 10111001010101110110010101001111 -$ yarng 5 +$ ./yarng 5 10011 ``` -Why I think this is obfuscated ------------------------------- +### Why I think this is obfuscated - Ever seen a 'do for ... while' loop? -- I avoided 'int' like the plague. Instead I used storage class specifiers -(register, auto) to get implicit int. The Standard allows implicit int even in +- I avoided `int` like the plague. Instead I used storage class specifiers +(`register`, `auto`) to get implicit int. The Standard allows implicit int even in casts as you can see in `(void(*)(register))main`. Where implicit int is impossible, like in the `int main` declaration I have int split across two lines. All indent programs I use insert space at the beginning of the @@ -148,7 +167,7 @@ continuation line and thereby introduce a syntax error. - `main` (ab)used as a signal handler. Shocking. Yeah, this leads to undefined behaviour. I have yet to see a system where it does not work. If it doesn't work -for you, I'd appreciate if you mail me about it. Uh-oh, schweikh did it, +for you, I'd appreciate if you mail me about it. Uh-oh, Schweikh did it, uttered "Works for me". Don't quote me on that! - Even if you know how the program works, you just can't predict the output. @@ -159,7 +178,7 @@ uttered "Works for me". Don't quote me on that! preprocessor directive does the trick. But saying `#line 10 "01\n"` is a little lame and I came up with `??=line 10 ONE(O(1,1,2,6,0,6))`. -- `__LINE__` is used as the signal number argument to signal(). If indenting or +- `__LINE__` is used as the signal number argument to `signal()`. If indenting or other editing changes the number of lines the program is likely to be killed after one second... Thanks to POSIX for specifying SIGALRM as 14. You're SOL if your system does not conform. Get a real OS. @@ -175,7 +194,7 @@ this line and prepare for a core dump. and as a plain identifier in `main`'s parameters. The rule is that whenever `ONE` is followed by `(` it must be the macro. -- A quote from Kernighan and Plauger, "The Elements of Programming Style", 2nd +- A quote from Kernighan and Plauger, _The Elements of Programming Style_, 2nd Ed., page 21: "A useful way to decide if some piece of code is clear or not is the 'telephone test.' If someone could understand your code when read aloud over the telephone, it's clear enough. If not then it needs rewriting." Now try @@ -184,8 +203,7 @@ the telephone test for 'one = zero = atoi (ONE[zero-1])'. - Don't you love the aesthetics of symmetry: `write (1, 1+__FILE__+1, 1)` (telephone test this as well; is it 1, One, ONE, one? Maybe won?). -Where does the randomness come from? ------------------------------------- +### Where does the randomness come from? Each bit obviously depends on the number of times the loop body is executed between two calls of the signal handler. But what determines @@ -196,24 +214,24 @@ this number? - On multitasking OS's: The total time the process is scheduled to run between successive invocations of the signal handler. -How about the randomness of the yarng? To measure these properties I +How about the randomness of the `yarng`? To measure these properties I counted the number of bit sequences and compared them to what I would expect from a generator with uniform distribution (all sequences equally likely to occur). -It is interesting to note that yarng's maximum deviations are less -than or equal to rand()'s. Randomness however tends to degrade under +It is interesting to note that `yarng`'s maximum deviations are less +than or equal to `rand()`'s. Randomness however tends to degrade under high load averages on my system (Linux). This could be avoided by allowing the process one second of execution time instead of wall clock time (using the `SIGVTALRM` sent by the virtual timer instead of `SIGALRM`). -I'm not surprised. Yarng in the end depends on fluctuations of the +I'm not surprised. `Yarng` in the end depends on fluctuations of the electrical field and the heat distribution in the oscillators, the implementation and state of the scheduling algorithm, the system load, number and temporal distribution of asynchronous events and last but not least the phase of the moon. God _does_ play dice. -Type yarng and watch Him roll. +Type `yarng` and watch Him roll. ## Copyright and CC BY-SA 4.0 License: