Comment 4 for bug 713985

This boils down to eglibc working with 8-byte floats on ARM, even if it's declared long double.
To see this behaviour on x86, build and run the following:

#include <stdio.h>
#include <math.h>
int main ()
{
  double x = 6.0;
  printf("sizof(double)=%d\n",sizeof(double));
  printf("lgamma (%.20f)=%.20f\n", x, lgamma(x));
  printf("tgamma (%.20f)=%.20f\n", x, tgamma(x));
  printf("exp(lgamma) (%.20f)=%.20f\n", x, exp(lgamma(x)));
  return 0;
}

On eglibc you'll see:

sizof(double)=8
lgamma (6.00000000000000000000)=4.78749174278204581157
tgamma (6.00000000000000000000)=119.99999999999997157829
exp(lgamma) (6.00000000000000000000)=119.99999999999997157829

On a better libc (MacOSX 10.6 on x86_64):

sizof(double)=8
lgamma (6.00000000000000000000)=4.78749174278204492339
tgamma (6.00000000000000000000)=120.00000000000000000000
exp(lgamma) (6.00000000000000000000)=119.99999999999987210231

So eglibc does a bad job computing gamma() on double (i.e. on 8-byte floats) in this range of values (around 6.0).