sys/external/bsd/compiler_rt/dist/lib/builtins/ppc/fixunstfdi.c

   1 /* This file is distributed under the University of Illinois Open Source
   2  * License. See LICENSE.TXT for details.
   3  */
   4
   5 /* uint64_t __fixunstfdi(long double x); */
   6 /* This file implements the PowerPC 128-bit double-double -> uint64_t conversion */
   7
   8 #include "DD.h"
   9
  10 uint64_t __fixunstfdi(long double input)
  11 {
  12         const DD x = { .ld = input };
  13         const doublebits hibits = { .d = x.s.hi };
  14
  15         const uint32_t highWordMinusOne = (uint32_t)(hibits.x >> 32) - UINT32_C(0x3ff00000);
  16
  17         /* If (1.0 - tiny) <= input < 0x1.0p64: */
  18         if (UINT32_C(0x04000000) > highWordMinusOne)
  19         {
  20                 const int unbiasedHeadExponent = highWordMinusOne >> 20;
  21
  22                 uint64_t result = hibits.x & UINT64_C(0x000fffffffffffff); /* mantissa(hi) */
  23                 result |= UINT64_C(0x0010000000000000); /* matissa(hi) with implicit bit */
  24                 result <<= 11; /* mantissa(hi) left aligned in the int64 field. */
  25
  26                 /* If the tail is non-zero, we need to patch in the tail bits. */
  27                 if (0.0 != x.s.lo)
  28                 {
  29                         const doublebits lobits = { .d = x.s.lo };
  30                         int64_t tailMantissa = lobits.x & INT64_C(0x000fffffffffffff);
  31                         tailMantissa |= INT64_C(0x0010000000000000);
  32
  33                         /* At this point we have the mantissa of |tail| */
  34
  35                         const int64_t negationMask = ((int64_t)(lobits.x)) >> 63;
  36                         tailMantissa = (tailMantissa ^ negationMask) - negationMask;
  37
  38                         /* Now we have the mantissa of tail as a signed 2s-complement integer */
  39
  40                         const int biasedTailExponent = (int)(lobits.x >> 52) & 0x7ff;
  41
  42                         /* Shift the tail mantissa into the right position, accounting for the
  43                          * bias of 11 that we shifted the head mantissa by.
  44                          */
  45                         tailMantissa >>= (unbiasedHeadExponent - (biasedTailExponent - (1023 - 11)));
  46
  47                         result += tailMantissa;
  48                 }
  49
  50                 result >>= (63 - unbiasedHeadExponent);
  51                 return result;
  52         }
  53
  54         /* Edge cases are handled here, with saturation. */
  55         if (1.0 > x.s.hi)
  56                 return UINT64_C(0);
  57         else
  58                 return UINT64_MAX;
  59 }