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[ltsmaster] Fix Issue 14786 - std.math.pow sometimes gets the sign of… #56

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redstar merged 1 commit into from
Feb 20, 2018
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[ltsmaster] Fix Issue 14786 - std.math.pow sometimes gets the sign of… #56

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35 changes: 31 additions & 4 deletions std/math.d
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Original file line number Diff line number Diff line change
Expand Up @@ -6837,12 +6837,30 @@ Unqual!(Largest!(F, G)) pow(F, G)(F x, G y) @nogc @trusted pure nothrow
{
// Result is real only if y is an integer
// Check for a non-zero fractional part
if (y > -1.0 / real.epsilon && y < 1.0 / real.epsilon)
enum maxOdd = pow(2.0L, real.mant_dig) - 1.0L;
static if (maxOdd > ulong.max)
{
long w = cast(long)y;
if (w != y)
// Generic method, for any FP type
if (floor(y) != y)
return sqrt(x); // Complex result -- create a NaN
if (w & 1) sign = -1.0;

const hy = ldexp(y, -1);
if (floor(hy) != hy)
sign = -1.0;
}
else
{
// Much faster, if ulong has enough precision
const absY = fabs(y);
if (absY <= maxOdd)
{
const uy = cast(ulong) absY;
if (uy != absY)
return sqrt(x); // Complex result -- create a NaN

if (uy & 1)
sign = -1.0;
}
}
x = -x;
}
Expand Down Expand Up @@ -6920,6 +6938,15 @@ Unqual!(Largest!(F, G)) pow(F, G)(F x, G y) @nogc @trusted pure nothrow
assert(isIdentical(pow(0.0, 6.0), 0.0));
assert(isIdentical(pow(-0.0, 6.0), 0.0));

// Issue #14786 fixed
immutable real maxOdd = pow(2.0L, real.mant_dig) - 1.0L;
assert(pow(-1.0L, maxOdd) == -1.0L);
assert(pow(-1.0L, -maxOdd) == -1.0L);
assert(pow(-1.0L, maxOdd + 1.0L) == 1.0L);
assert(pow(-1.0L, -maxOdd + 1.0L) == 1.0L);
assert(pow(-1.0L, maxOdd - 1.0L) == 1.0L);
assert(pow(-1.0L, -maxOdd - 1.0L) == 1.0L);

// Now, actual numbers.
assert(approxEqual(pow(two, three), 8.0));
assert(approxEqual(pow(two, -2.5), 0.1767767));
Expand Down