compiler-rt/lib/builtins/ppc/gcc_qmul.c

   1 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   2 // See https://llvm.org/LICENSE.txt for license information.
   3 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   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 #include "DD.h"
  10
  11 long double __gcc_qmul(long double x, long double y) {
  12   static const uint32_t infinityHi = UINT32_C(0x7ff00000);
  13   DD dst = {.ld = x}, src = {.ld = y};
  14
  15   register double A = dst.s.hi, a = dst.s.lo, B = src.s.hi, b = src.s.lo;
  16
  17   double aHi, aLo, bHi, bLo;
  18   double ab, tmp, tau;
  19
  20   ab = A * B;
  21
  22   // Detect special cases
  23   if (ab == 0.0) {
  24     dst.s.hi = ab;
  25     dst.s.lo = 0.0;
  26     return dst.ld;
  27   }
  28
  29   const doublebits abBits = {.d = ab};
  30   if (((uint32_t)(abBits.x >> 32) & infinityHi) == infinityHi) {
  31     dst.s.hi = ab;
  32     dst.s.lo = 0.0;
  33     return dst.ld;
  34   }
  35
  36   // Generic cases handled here.
  37   aHi = high26bits(A);
  38   bHi = high26bits(B);
  39   aLo = A - aHi;
  40   bLo = B - bHi;
  41
  42   tmp = LOWORDER(ab, aHi, aLo, bHi, bLo);
  43   tmp += (A * b + a * B);
  44   tau = ab + tmp;
  45
  46   dst.s.lo = (ab - tau) + tmp;
  47   dst.s.hi = tau;
  48
  49   return dst.ld;
  50 }