lib/ppc/gcc_qmul.c

   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
  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 }