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Fix issue 16026: std.math.frexp!float() wrong for very small subnormals #4337

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Merged
dnadlinger merged 1 commit into from
May 22, 2016
Merged

Fix issue 16026: std.math.frexp!float() wrong for very small subnormals #4337

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19 changes: 11 additions & 8 deletions std/math.d
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Original file line number Diff line number Diff line change
Expand Up @@ -2406,7 +2406,7 @@ T frexp(T)(const T value, out int exp) @trusted pure nothrow @nogc
vf *= F.RECIP_EPSILON;
ex = vu[F.EXPPOS_SHORT] & F.EXPMASK;
exp = ex - F.EXPBIAS - T.mant_dig + 1;
vu[F.EXPPOS_SHORT] = (0x8000 & vu[F.EXPPOS_SHORT]) | 0x3FFE;
vu[F.EXPPOS_SHORT] = (~F.EXPMASK & vu[F.EXPPOS_SHORT]) | 0x3FFE;
}
return vf;
}
Expand Down Expand Up @@ -2449,7 +2449,7 @@ T frexp(T)(const T value, out int exp) @trusted pure nothrow @nogc
ex = vu[F.EXPPOS_SHORT] & F.EXPMASK;
exp = ex - F.EXPBIAS - T.mant_dig + 1;
vu[F.EXPPOS_SHORT] =
cast(ushort)((0x8000 & vu[F.EXPPOS_SHORT]) | 0x3FFE);
cast(ushort)((~F.EXPMASK & vu[F.EXPPOS_SHORT]) | 0x3FFE);
}
return vf;
}
Expand Down Expand Up @@ -2489,7 +2489,7 @@ T frexp(T)(const T value, out int exp) @trusted pure nothrow @nogc
ex = vu[F.EXPPOS_SHORT] & F.EXPMASK;
exp = ((ex - F.EXPBIAS) >> 4) - T.mant_dig + 1;
vu[F.EXPPOS_SHORT] =
cast(ushort)((0x8000 & vu[F.EXPPOS_SHORT]) | 0x3FE0);
cast(ushort)((~F.EXPMASK & vu[F.EXPPOS_SHORT]) | 0x3FE0);
}
return vf;
}
Expand Down Expand Up @@ -2529,7 +2529,7 @@ T frexp(T)(const T value, out int exp) @trusted pure nothrow @nogc
ex = vu[F.EXPPOS_SHORT] & F.EXPMASK;
exp = ((ex - F.EXPBIAS) >> 7) - T.mant_dig + 1;
vu[F.EXPPOS_SHORT] =
cast(ushort)((0x8000 & vu[F.EXPPOS_SHORT]) | 0x3F00);
cast(ushort)((~F.EXPMASK & vu[F.EXPPOS_SHORT]) | 0x3F00);
}
return vf;
}
Expand Down Expand Up @@ -2574,6 +2574,9 @@ unittest
tuple(-T.infinity, -T.infinity, int.min),
tuple(T.nan, T.nan, int.min),
tuple(-T.nan, -T.nan, int.min),

// Phobos issue #16026:
tuple(3 * (T.min_normal * T.epsilon), T( .75), (T.min_exp - T.mant_dig) + 2)
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@ibuclaw ibuclaw May 18, 2016

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Does the issue need to be included with the test?

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@tsbockman tsbockman May 18, 2016

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Well, it's just a comment, so obviously it doesn't need to be there. This is a common practice in the core dlang projects though: to label tests with the issue number that precipitated their inclusion.

Two main benefits I see:

  • Seeing issue labels like this scattered throughout the tests provides real-world evidence to people browsing the code about what kind of test cases are needed for full coverage of related algorithms. Without that feedback, it is hard to know when to stop adding test cases.
  • For anyone tempted to reduce the number of test cases while refactoring, or while trying to speed up the test suite, it says, "Don't remove this one!"

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@ibuclaw ibuclaw May 19, 2016

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No one should be removing tests though if they want to keep the coverage. ;-)

];

foreach (elem; vals)
Expand All @@ -2591,10 +2594,10 @@ unittest
static if (floatTraits!(T).realFormat == RealFormat.ieeeExtended)
{
static T[3][] extendedvals = [ // x,frexp,exp
[0x1.a5f1c2eb3fe4efp+73L, 0x1.A5F1C2EB3FE4EFp-1L, 74], // normal
[0x1.fa01712e8f0471ap-1064L, 0x1.fa01712e8f0471ap-1L, -1063],
[T.min_normal, .5, -16381],
[T.min_normal/2.0L, .5, -16382] // subnormal
[0x1.a5f1c2eb3fe4efp+73L, 0x1.A5F1C2EB3FE4EFp-1L, 74], // normal
[0x1.fa01712e8f0471ap-1064L, 0x1.fa01712e8f0471ap-1L, -1063],
[T.min_normal, .5, -16381],
[T.min_normal/2.0L, .5, -16382] // subnormal
];
foreach (elem; extendedvals)
{
Expand Down