lib/ppc/gcc_qmul.c

// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.

// long double __gcc_qmul(long double x, long double y);
// This file implements the PowerPC 128-bit double-double multiply operation.
// This implementation is shamelessly cribbed from Apple's DDRT, circa 1993(!)

#include "DD.h"

long double __gcc_qmul(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;
	
	double aHi, aLo, bHi, bLo;
    double ab, tmp, tau;
	
	ab = A * B;
	
	// Detect special cases
	if (ab == 0.0) {
		dst.hi = ab;
		dst.lo = 0.0;
		return dst.ld;
	}
	
	const doublebits abBits = { .d = ab };
	if (((uint32_t)(abBits.x >> 32) & infinityHi) == infinityHi) {
		dst.hi = ab;
		dst.lo = 0.0;
		return dst.ld;
	}
	
	// Generic cases handled here.
    aHi = high26bits(A);
    bHi = high26bits(B);
    aLo = A - aHi;
    bLo = B - bHi;
	
    tmp = LOWORDER(ab, aHi, aLo, bHi, bLo);
    tmp += (A * b + a * B);
    tau = ab + tmp;
	
    dst.lo = (ab - tau) + tmp;
    dst.hi = tau;
	
    return dst.ld;
}