Date: Mon, 19 Aug 2002 18:05:09 +0100 From: Matthew Seaman <m.seaman@infracaninophile.co.uk> To: Mikhail Teterin <mi+mx@aldan.algebra.com> Cc: Dan Nelson <dnelson@allantgroup.com>, Matthew Seaman <m.seaman@infracaninophile.co.uk>, questions@FreeBSD.ORG Subject: Re: pow(3) on FreeBSD Message-ID: <20020819170509.GA10906@happy-idiot-talk.infracaninophi> In-Reply-To: <200208191124.35129.mi%2Bmx@aldan.algebra.com> References: <200208190413.g7J4DEcw051123@corbulon.video-collage.com> <20020819043012.GN74231@dan.emsphone.com> <200208191124.35129.mi%2Bmx@aldan.algebra.com>
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On Mon, Aug 19, 2002 at 11:24:35AM -0400, Mikhail Teterin wrote:
> You are right, the FreeBSD's man-page does not specify the return value
> in case of a non-integer y. I just know it from experiment to be zero
> (and not NaN as Matthew claimed).
That was a non-integer power of a *negative* number... Anyhow, the
claim that NaN was returned was based on empirical evidence:
happy-idiot-talk:~/misc:% cat xpow.c
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <errno.h>
int
main(int argc, char *argv[])
{
double x;
double y;
double res;
if (argc < 3) {
fprintf(stderr, "%s", "Usage: pow x y\n");
exit(-1);
}
x = strtod(argv[1], NULL);
y = strtod(argv[2], NULL);
errno = 0;
res = pow(x, y);
if (errno) {
perror("pow() error: ");
}
printf("%g ^ %g = %g\n", x, y, res);
exit(0);
}
/* Compile: cc -o xpow xpow.c -lm */
happy-idiot-talk:~/misc:% cc -o xpow xpow.c -lm
happy-idiot-talk:~/misc:% ./xpow -1 0.5
-1 ^ 0.5 = NaN
Mind you, there's also the mysterious case of the errno that didn't
bark in the night. This is:
happy-idiot-talk:~/misc:% uname -v
FreeBSD 4.6-STABLE #3: Sat Aug 17 20:32:01 BST 2002 matthew@happy-idiot-talk.infracaninophile.co.uk:/usr/obj/usr/src/sys/HAPPY-IDIOT-TALK
running on:
happy-idiot-talk:~/misc:% grep CPU /var/run/dmesg.boot
CPU: AMD Athlon(TM) XP1600+ (1400.06-MHz 686-class CPU)
Cheers,
Matthew
--
Dr Matthew J Seaman MA, D.Phil. 26 The Paddocks
Savill Way
Tel: +44 1628 476614 Marlow
Fax: +44 0870 0522645 Bucks., SL7 1TH UK
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