Sourceware Bugzilla – Attachment 6004 Details for
Bug 13304
fma, fmaf, fmal produce wrong results
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test case #14 for fmal()
fma-bug14.c (text/x-csrc), 807 bytes, created by
Bruno Haible
on 2011-10-17 02:10:29 UTC
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Description:
test case #14 for fmal()
Filename:
MIME Type:
Creator:
Bruno Haible
Created:
2011-10-17 02:10:29 UTC
Size:
807 bytes
patch
obsolete
>/* Bug in fmal() of glibc 2.11.3 on x86_64. */ > >#include <math.h> >#include <stdio.h> > >int >main () >{ > volatile long double x = 1.0L + ldexpl (1.0L, -32); /* 2^0 + 2^-32 */ > volatile long double y = - x; > volatile long double z = ldexpl (1.0L, 34); /* 2^34 */ > /* x * y + z with infinite precision: 2^34 - (2^0 + 2^-31 + 2^-64). > Lies between (2^64 - 2^30 - 1) * 2^-30 and (2^64 - 2^30) * 2^-30 > and is closer to (2^64 - 2^30 - 1) * 2^-30, therefore the rounding > must round down and produce (2^64 - 2^30 - 1) * 2^-30. */ > volatile long double expected = z - 1.0L - ldexpl (1.0L, -30); > volatile long double result = fmal (x, y, z); > > if (result != expected) > { > printf ("Expected: %LA\n", expected); > printf ("Actual: %LA\n", result); > return 1; > } > > return 0; >}
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