Package: libc6
Version: 2.7-6
Severity: normal
File: glibc
On arm, compiling the following code with gcc-4.2
gives different results depending on whether the
flag -ansi is passed:
#include <float.h>
#include <ieee754.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
int main(void) {
union ieee754_double val;
uint64_t bits;
val.d = DBL_MAX;
bits = ((uint64_t) val.ieee.negative) << 63
| ((uint64_t) val.ieee.exponent) << 52
| ((uint64_t) val.ieee.mantissa0) << 32
| ((uint64_t) val.ieee.mantissa1);
printf("%llx\n", bits);
exit(EXIT_SUCCESS);
}
the good:
$ gcc-4.2 test-double.c
$ ./a.out
0x7fefffffffffffff
the bad:
$ gcc-4.2 -ansi test-double.c
$ ./a.out
0xffffffff7fefffff
i.e. the words are flipped around.
In a conversation on #debian-arm, pbrooks noted that
the tests in file ieee754.h whether to flip the
mantissa bits (which is necessary on arm) depends
on BIG_ENDIAN, instead of __BIG_ENDIAN.
Defining BIG_ENDIAN as __BIG_ENDIAN makes the code
print out the expected result.
This seems to be an upstream issue, too. A fix could
be to patch sysdeps/ieee754/ieee754.h to use __BIG_ENDIAN
everywhere.
-- System Information:
Debian Release: lenny/sid
APT prefers unstable
APT policy: (500, 'unstable')
Architecture: arm (armv5tejl)
Kernel: Linux 2.6.18-4-versatile
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=locale: Cannot set
LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
ANSI_X3.4-1968)
Shell: /bin/sh linked to /bin/bash
Versions of packages libc6 depends on:
ii libgcc1 1:4.3-20080127-1 GCC support library
libc6 recommends no packages.
-- debconf information excluded
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