Re: [Chicken-users] expt incorrect in boundary cases

[fulvio ciriaco]

No, not a bug with the definition.
It depends on libm.
>csi -e "(print (expt 1.0 +inf))" 
1.0
>uname -a
Linux bellini 2.6.28-ARCH #1 SMP PREEMPT Sun Mar 8 10:18:28 UTC 2009 i686 AMD 
Athlon(tm) 64 Processor 3200+ AuthenticAMD GNU/Linux
>ldd chicken/bin/csi
        linux-gate.so.1 =>  (0xb7f10000)
        libchicken.so => /home/fc/chicken/lib/libchicken.so (0xb7ca6000)
        libm.so.6 => /lib/libm.so.6 (0xb7c67000)
        libdl.so.2 => /lib/libdl.so.2 (0xb7c63000)
        libc.so.6 => /lib/libc.so.6 (0xb7b1c000)
        /lib/ld-linux.so.2 (0xb7f11000)

>csi -e "(print (expt 1.0 +inf))" 
+nan
>uname -a
>ldd chicken/bin/csi
        -lc.12 => /usr/lib/libc.so.12
        -lm.0 => /usr/lib/libm.so.0
        -lchicken => /home/fc/chicken/lib/libchicken.so

NetBSD  5.0_RC4 NetBSD 5.0_RC4 (GENERIC) #0: Wed Apr 15 12:24:14 UTC 2009  
address@hidden:/home/builds/ab/netbsd-5-0-RC4/i386/200904142015Z-obj/home/builds/ab/netbsd-5-0-RC4/src/sys/arch/i386/compile/GENERIC
 i386

Fulvio

From: John Cowan <address@hidden>
Subject: [Chicken-users] expt incorrect in boundary cases
Date: Tue, 28 Apr 2009 11:14:46 -0400

> According to IEEE 754, the four expressions (expt 1.0 +inf), (expt -1.0 +inf),
> (expt 1.0 -inf), and (expt -1.0 -inf) should all return +nan.  In Chicken they
> all return 1.0 instead.  This appears to be a bug in the ISO C definition
> of the "pow" function.  Checking for these four cases and bypassing pow
> would Do The Right Thing.
> 
> I found this when exhaustively checking the boundary cases for abs, acos,
> asin, atan (1-arg and 2-arg versions), ceiling, cos, exp, expt, floor, log,
> round, sin, sqrt, and tan.  All the others are correct.
> 
> -- 
> John Cowan        http://ccil.org/~cowan   address@hidden
> Lope de Vega: "It wonders me I can speak at all.  Some caitiff rogue did
> rudely yerk me on the knob, wherefrom my wits still wander."
> An Englishman: "Ay, a filchman to the nab betimes 'll leave a man
> crank for a spell." --Harry Turtledove, Ruled Britannia
> 
> 
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