Date: Mon, 19 Aug 2002 11:24:35 -0400 From: Mikhail Teterin <mi+mx@aldan.algebra.com> To: Dan Nelson <dnelson@allantgroup.com>, Matthew Seaman <m.seaman@infracaninophile.co.uk> Cc: questions@FreeBSD.ORG Subject: Re: pow(3) on FreeBSD Message-ID: <200208191124.35129.mi%2Bmx@aldan.algebra.com> In-Reply-To: <20020819043012.GN74231@dan.emsphone.com> References: <200208190413.g7J4DEcw051123@corbulon.video-collage.com> <20020819043012.GN74231@dan.emsphone.com>
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On Monday 19 August 2002 12:30 am, Dan Nelson wrote:
= In the last episode (Aug 19), Mikhail Teterin said:
= > In accordance with its man-page entry, pow(3) will return 0 if its
= > second argument is not an integer. Why is that? What's the reasoning
= > and what is a workaround -- I'm trying to port an application from
= > Solaris, which uses pow(3) quite heavily...
= Seems to work fine for me. Where in the manpage does it say that? All
= I can see is that if x<0, y must be an integer.
= My Solaris manpage says the same thing.
No, it does not have the requirement of y being an integer. Only that x
is positive.
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).
= $ cat > test.c
= #include <math.h>
= #include <stdio.h>
= main()
= {
= printf("%f\n", pow(2, 1.5));
= }
= ^D
= $ gcc test.c -lm
= $ ./a.out
= 2.828427
The test above was, obviously, done on Solaris. On FreeBSD, this same
program outputs zero:
mteterin@misha:~ (257) uname -a
FreeBSD misha 5.0-CURRENT FreeBSD 5.0-CURRENT #0: Wed Jul 31 13:27:39 EDT
2002 mteterin@misha [...]
mteterin@misha:~ (258) ./a.out
0.000000
mteterin@attila:~ (515) uname -a
SunOS attila 5.8 Generic_108528-13 sun4u sparc SUNW,Sun-Fire-280R
mteterin@attila:~ (516) ./a.out
2.828427
On Monday 19 August 2002 03:10 am, Matthew Seaman wrote:
= No --- read the manual page again more carefully. It says:
=
= The functions pow(x, y) checks to see if x < 0 and y is not an integer
= Or in other words, pow() returns NaN and sets errno == EDOM in
= situations where the result would be complex valued.
This is just not true. I guess, questions@ needs a moderator :-/ to keep
poor quality help out and angry insulting responses (such as this one by
me) muted! The man-page does not mention NaN (Not-a-Number) at all:
mteterin@misha:~ (265) man 3 pow | fgrep NaN | wc -l
0
= > Needless to say, Solaris' pow works properly for non-integer
= > arguments...
= Even Solaris cannot return a complex value as a double.
There is nothing complex (pun intended) about, say, 1^2.5. It is still
1. -- unless you are running FreeBSD (Linux?)... There is nothing
complex about Dan's's example (2^1.5) above either -- the correct value
is 2.828427, but it is 0 on FreeBSD -- in accordance with the man-page
and in disagreement with Dan...
Now, can someone, please, offer the REAL reasons for the FreeBSD's
apparent defficiency? May be, even a double-precision workaround --
unlike powf(3), which operates on float-precision numbers?..
Thank you!
-mi
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