compiler-rt/lib/builtins/ppc/floatunditf.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 __floatunditf(unsigned long long x);
   6 // This file implements the PowerPC unsigned long long -> long double conversion
   7
   8 #include "DD.h"
   9
  10 long double __floatunditf(uint64_t a) {
  11
  12   // Begins with an exact copy of the code from __floatundidf
  13
  14   static const double twop52 = 0x1.0p52;
  15   static const double twop84 = 0x1.0p84;
  16   static const double twop84_plus_twop52 = 0x1.00000001p84;
  17
  18   doublebits high = {.d = twop84};
  19   doublebits low = {.d = twop52};
  20
  21   high.x |= a >> 32;                         // 0x1.0p84 + high 32 bits of a
  22   low.x |= a & UINT64_C(0x00000000ffffffff); // 0x1.0p52 + low 32 bits of a
  23
  24   const double high_addend = high.d - twop84_plus_twop52;
  25
  26   // At this point, we have two double precision numbers
  27   // high_addend and low.d, and we wish to return their sum
  28   // as a canonicalized long double:
  29
  30   // This implementation sets the inexact flag spuriously.
  31   // This could be avoided, but at some substantial cost.
  32
  33   DD result;
  34
  35   result.s.hi = high_addend + low.d;
  36   result.s.lo = (high_addend - result.s.hi) + low.d;
  37
  38   return result.ld;
  39 }