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From: braner@batcomputer.TN.CORNELL.EDU (braner)
Newsgroups: net.micro.amiga,net.micro.atari16
Subject: Re: C compiler bugs
Message-ID: <737@batcomputer.TN.CORNELL.EDU>
Date: Sat, 26-Jul-86 21:39:30 EDT
Article-I.D.: batcompu.737
Posted: Sat Jul 26 21:39:30 1986
Date-Received: Sun, 27-Jul-86 06:08:20 EDT
References: <888@ucbcad.BERKELEY.EDU> <678@batcomputer.TN.CORNELL.EDU>
Reply-To: braner@batcomputer.UUCP (braner)
Organization: Theory Center, Cornell University, Ithaca NY
Lines: 92
Xref: mnetor net.micro.amiga:4014 net.micro.atari16:1407

[]

The compiler bugs (especially in the floating-point package) keep
wasting my time... - here are some tidbits that might save YOU some time:

The Megamax library does not have a fabs() function, and abs()
does not always work right for FP. So I added this to math.h:

	#define fabs(x) (((x)<0.0)?(-(x)):(x))

The transcendental functions do NOT warn you if the argument passed to
them is illegal. You get GARBAGE (and you don't even know it!), or it
crashes, or (in the case of log(0)) it HANGS!

I now use LOG() and SQRT() instead of log() and sqrt(). The following
functions were also added to math.h:

	double LOG(x)
		double x;
	{
		if (x <= 0.0) {
			fprintf(stderr,"illegal arg for log()!\n");
			exit(0);
		}
		x = log(x);
		return (x);
	}

	double SQRT(x)
		double x;
	{
		if (x < 0.0) {
			fprintf(stderr,"illegal arg for sqrt()!\n");
			exit(0);
		}
		x = sqrt(x);
		return (x);
	}

If your program gets into an infinite loop, or just a loop that's too long,
there is no way to stop it unless it's doing I/O. To enable that, add the
statement "keybrk();" here and there in your loops, and #include the
following file at the top of your source:

	/* Check if a key has been pressed, and if it was
	 * a control-C print message and exit
	 */

	#include <osbind.h>

	keybrk()
	{
		if (Cconis()) {				/* any key pressed? */
			if ((Crawcin()&0x7F) == 0x03) {	/* is it ctrl-C?    */
				fputs("\nbreak!\n\n", stderr);
				exit(0);
			}
		}
	}

Finally, the simple random-number generator, defined as a macro in stdio.h:

	extern long _seed;
	#define srand(x) _seed = x;
	#define rand() (int)(_seed * 6907 + 130253)

is no good because a call to rand() does not update _seed, so you keep
getting the same nonrandom number again and again! Change to:

	#define rand() (int)(_seed = (_seed * 6907 + 130253))

Don't forget to do an srand(SEED), with SEED some integer, or else you'll
get the same sequence each time you run the program. For an unpredictable
sequence (good in games, for example) use the current (encoded!) time
as SEED!

If you want a floating-point version, returning a number between 0 & 1:

	#define RND  ((double)(rand())/65536.0 + 0.5)

(But I would NOT recommend this kind of random number generator for
 serious statistical purposes!)

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	- Moshe Braner

	Corson Hall, Cornell University, Ithaca NY 14853
	(607) 272-3487
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