[PPL-devel] More floating point problems on the Alpha

[Roberto Bagnara]

[Thanks to all those who responded to my previous problem-report
wrt to the IEEE inexact-flag on the Alpha.  We have filed a bug
report for that one.]

Hi there,

we keep finding problems on the Alpha, and we are unsure about
what is going on.  I anticipate that the present problem does
not seem to be a compiler issue (except that the -mieee-with-inexact
option promises full compliance with the IEEE floating point
standard).  However, I hope some Alpha expert can advise about
how to investigate the issue further.

Here are the details:

$ cat bug.c
#include <stdio.h>

float f = 1.4e-45;
double d = 1e-300;

int
main() {
   if (1.4e-45f > 1e-300)
     printf("compile-time test says 1.4e-45f > 1e-300\n");
   if (f < d)
     printf("    run-time test says 1.4e-45f < 1e-300\n");
   return 0;
}

$ gcc -mieee-with-inexact bug.c

$ ./a.out
compile-time test says 1.4e-45f > 1e-300
     run-time test says 1.4e-45f < 1e-300

$ gcc -v
Using built-in specs.
Target: alpha-linux-gnu
Configured with: ../src/configure -v --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --enable-nls --with-gxx-include-dir=/usr/include/c++/4.2 --program-suffix=-4.2 --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --enable-mpfr --disable-libssp --with-long-double-128 --enable-checking=release --build=alpha-linux-gnu --host=alpha-linux-gnu --target=alpha-linux-gnu
Thread model: posix
gcc version 4.2.4 (Debian 4.2.4-3)

$ cat /proc/cpuinfo
cpu                     : Alpha
cpu model               : EV56
cpu variation           : 7
cpu revision            : 0
cpu serial number       :
system type             : Rawhide
system variation        : Tincup
system revision         : 0
system serial number    : AY74642662
cycle frequency [Hz]    : 399642346 est.
timer frequency [Hz]    : 1200.00
page size [bytes]       : 8192
phys. address bits      : 40
max. addr. space #      : 127
BogoMIPS                : 705.16
kernel unaligned acc    : 0 (pc=0,va=0)
user unaligned acc      : 35 (pc=20000074c18,va=87)
platform string         : AlphaServer 1200 5/400 4MB
cpus detected           : 1
cpus active             : 1
cpu active mask         : 0000000000000001
L1 Icache               : 8K, 1-way, 32b line
L1 Dcache               : 8K, 1-way, 32b line
L2 cache                : 96K, 3-way, 64b line
L3 cache                : 4096K, 1-way, 64b line

All the best,

     Roberto

-- 
Prof. Roberto Bagnara
Computer Science Group
Department of Mathematics, University of Parma, Italy
http://www.cs.unipr.it/~bagnara/
mailto:bagnara at cs.unipr.it