reldiff bug in GMP 4.1.2 unpatched (and also 4.1.3 unpatched)

[abbott]

Hi,

VERBAL SUMMARY:
  reldiff unexpectedly gives zero

PLATFORM
Linux point 2.4.22 #1 Thu Sep 11 12:43:28 UTC 2003 i686 unknown

COMPILER
Reading specs from /usr/lib/gcc-lib/i386-slackware-linux/3.2.2/specs
Configured with: ../gcc-3.2.2/configure --prefix=/usr --enable-shared
--enable-threads=posix --enable-__cxa_atexit --disable-checking
--with-gnu-ld --verbose --target=i386-slackware-linux
--host=i386-slackware-linux
Thread model: posix
gcc version 3.2.2


PROGRAM EXHIBITING BUG: (C++ source)
#include <gmp.h>
#include <iostream>

using namespace std;

int main()
{
  mpf_t a, b, rd;
  mpf_init2(a, 128);       // ask for 128 bits' precision
  mpf_init2(b, 128);       // again
  mpf_init2(rd, 8);        // I don't need much precision here

  mpf_set_ui(a, 1);        // a = 1
  mpf_set_ui(b, 1);
  mpf_div_2exp(b, b, 65);
  mpf_add(b, b, a);        // b = 1 + 2^(-65)

  mpf_reldiff(rd, a, b);   // should be about 2^(-65), but gives zero
  double mant;
  long exp;
  mant = mpf_get_d_2exp(&exp, rd);
  cout << "reldiff is approx " << mant << " times 2^(" << exp << ")" << endl;

  return 0;
}