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Remove slow array copy from math.floor()

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This commit is contained in:
Iain Buclaw 2014-06-27 07:44:11 +01:00
parent 2278751883
commit df5dab4a7a
1 changed files with 18 additions and 12 deletions
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30
std/math.d
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@ -3079,12 +3079,20 @@ real floor(real x) @trusted pure nothrow @nogc
return x;
alias F = floatTraits!(real);
auto vu = *cast(ushort[real.sizeof/2]*)(&x);
// Take care not to trigger library calls from the compiler,
// while ensuring that we don't get defeated by some optimizers.
union realBits
{
real rv;
ushort[real.sizeof/2] vu;
}
realBits y = void;
y.rv = x;
// Find the exponent (power of 2)
static if (real.mant_dig == 53)
{
int exp = ((vu[F.EXPPOS_SHORT] >> 4) & 0x7ff) - 0x3ff;
int exp = ((y.vu[F.EXPPOS_SHORT] >> 4) & 0x7ff) - 0x3ff;
version (LittleEndian)
int pos = 0;
@ -3093,7 +3101,7 @@ real floor(real x) @trusted pure nothrow @nogc
}
else static if (real.mant_dig == 64)
{
int exp = (vu[F.EXPPOS_SHORT] & 0x7fff) - 0x3fff;
int exp = (y.vu[F.EXPPOS_SHORT] & 0x7fff) - 0x3fff;
version (LittleEndian)
int pos = 0;
@ -3102,7 +3110,7 @@ real floor(real x) @trusted pure nothrow @nogc
}
else if (real.mant_dig == 113)
{
int exp = (vu[F.EXPPOS_SHORT] & 0x7fff) - 0x3fff;
int exp = (y.vu[F.EXPPOS_SHORT] & 0x7fff) - 0x3fff;
version (LittleEndian)
int pos = 0;
@ -3126,22 +3134,20 @@ real floor(real x) @trusted pure nothrow @nogc
while (exp >= 16)
{
version (LittleEndian)
vu[pos++] = 0;
y.vu[pos++] = 0;
else
vu[pos--] = 0;
y.vu[pos--] = 0;
exp -= 16;
}
// Clear the remaining bits.
if (exp > 0)
vu[pos] &= BMASK[exp];
y.vu[pos] &= BMASK[exp];
real y = *cast(real*)(&vu);
if ((x < 0.0) && (x != y.rv))
y.rv -= 1.0;
if ((x < 0.0) && (x != y))
y -= 1.0;
return y;
return y.rv;
}
}