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Make std.math.isIdentical work in CTFE #7515

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Make std.math.isIdentical work in CTFE #7515

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33 changes: 33 additions & 0 deletions std/math.d
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Original file line number Diff line number Diff line change
Expand Up @@ -6418,6 +6418,27 @@
*/
bool isIdentical(real x, real y) @trusted pure nothrow @nogc
{
if (__ctfe)
{
if (x !is y) return false;

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if (x == x) return true; // If not NaN `is` implies identical representation.
static if (double.mant_dig != real.mant_dig)
{
// Works because we are in CTFE and there is no way in CTFE to set more
// bits of NaN payload than can fit in a double, and since 2.087
// changed real.init to be non-signaling I *think* there is no way in
// CTFE for a real to be a signaling NaN unless real and double have
// the same representation so real's bits can be manipulated directly.
double d1 = x, d2 = y;

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}
else
{
// Alias to avoid converting signaling to quiet.
alias d1 = x;
alias d2 = y;
}
return *cast(long*) &d1 == *cast(long*) &d2;

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}
// We're doing a bitwise comparison so the endianness is irrelevant.
long* pxs = cast(long *)&x;
long* pys = cast(long *)&y;
Expand Down Expand Up @@ -6455,6 +6476,18 @@
assert(!isIdentical(real.infinity, -real.infinity));
}

@safe @nogc pure nothrow unittest
{
static assert( isIdentical(0.0, 0.0));
static assert( isIdentical(1.0, 1.0));
static assert( isIdentical(real.infinity, real.infinity));
static assert( isIdentical(-real.infinity, -real.infinity));
static assert( isIdentical(real.nan, real.nan));

static assert(!isIdentical(0.0, -0.0));
static assert(!isIdentical(real.nan, -real.nan));
static assert(!isIdentical(real.infinity, -real.infinity));
}
/*********************************
* Return 1 if sign bit of e is set, 0 if not.
*/
Expand Down