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1 /* This file is distributed under the University of Illinois Open Source
2  * License. See LICENSE.TXT for details.
3  */
4 
5 /* long double __gcc_qmul(long double x, long double y);
6  * This file implements the PowerPC 128-bit double-double multiply operation.
7  * This implementation is shamelessly cribbed from Apple's DDRT, circa 1993(!)
8  */
9 
10 #include "DD.h"
11 
__gcc_qmul(long double x,long double y)12 long double __gcc_qmul(long double x, long double y)
13 {
14 	static const uint32_t infinityHi = UINT32_C(0x7ff00000);
15 	DD dst = { .ld = x }, src = { .ld = y };
16 
17 	register double A = dst.s.hi, a = dst.s.lo,
18 					B = src.s.hi, b = src.s.lo;
19 
20 	double aHi, aLo, bHi, bLo;
21     double ab, tmp, tau;
22 
23 	ab = A * B;
24 
25 	/* Detect special cases */
26 	if (ab == 0.0) {
27 		dst.s.hi = ab;
28 		dst.s.lo = 0.0;
29 		return dst.ld;
30 	}
31 
32 	const doublebits abBits = { .d = ab };
33 	if (((uint32_t)(abBits.x >> 32) & infinityHi) == infinityHi) {
34 		dst.s.hi = ab;
35 		dst.s.lo = 0.0;
36 		return dst.ld;
37 	}
38 
39 	/* Generic cases handled here. */
40     aHi = high26bits(A);
41     bHi = high26bits(B);
42     aLo = A - aHi;
43     bLo = B - bHi;
44 
45     tmp = LOWORDER(ab, aHi, aLo, bHi, bLo);
46     tmp += (A * b + a * B);
47     tau = ab + tmp;
48 
49     dst.s.lo = (ab - tau) + tmp;
50     dst.s.hi = tau;
51 
52     return dst.ld;
53 }
54