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// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// long double __gcc_qsub(long double x, long double y);
// This file implements the PowerPC 128-bit double-double add operation.
// This implementation is shamelessly cribbed from Apple's DDRT, circa 1993(!)
#include "DD.h"
long double __gcc_qsub(long double x, long double y)
{
static const uint32_t infinityHi = UINT32_C(0x7ff00000);
DD dst = { .ld = x }, src = { .ld = y };
register double A = dst.hi, a = dst.lo,
B = -src.hi, b = -src.lo;
// If both operands are zero:
if ((A == 0.0) && (B == 0.0)) {
dst.hi = A + B;
dst.lo = 0.0;
return dst.ld;
}
// If either operand is NaN or infinity:
const doublebits abits = { .d = A };
const doublebits bbits = { .d = B };
if ((((uint32_t)(abits.x >> 32) & infinityHi) == infinityHi) ||
(((uint32_t)(bbits.x >> 32) & infinityHi) == infinityHi)) {
dst.hi = A + B;
dst.lo = 0.0;
return dst.ld;
}
// If the computation overflows:
// This may be playing things a little bit fast and loose, but it will do for a start.
const double testForOverflow = A + (B + (a + b));
const doublebits testbits = { .d = testForOverflow };
if (((uint32_t)(testbits.x >> 32) & infinityHi) == infinityHi) {
dst.hi = testForOverflow;
dst.lo = 0.0;
return dst.ld;
}
double H, h;
double T, t;
double W, w;
double Y;
H = B + (A - (A + B));
T = b + (a - (a + b));
h = A + (B - (A + B));
t = a + (b - (a + b));
if (fabs(A) <= fabs(B))
w = (a + b) + h;
else
w = (a + b) + H;
W = (A + B) + w;
Y = (A + B) - W;
Y += w;
if (fabs(a) <= fabs(b))
w = t + Y;
else
w = T + Y;
dst.hi = Y = W + w;
dst.lo = (W - Y) + w;
return dst.ld;
}
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