src/libcompiler_builtins/compiler-rt/lib/builtins/ppc/fixtfdi.c

   1 /* This file is distributed under the University of Illinois Open Source
   2  * License. See LICENSE.TXT for details.
   3  */
   4
   5 /* int64_t __fixunstfdi(long double x);
   6  * This file implements the PowerPC 128-bit double-double -> int64_t conversion
   7  */
   8
   9 #include "DD.h"
  10 #include "../int_math.h"
  11
  12 uint64_t __fixtfdi(long double input)
  13 {
  14         const DD x = { .ld = input };
  15         const doublebits hibits = { .d = x.s.hi };
  16
  17         const uint32_t absHighWord = (uint32_t)(hibits.x >> 32) & UINT32_C(0x7fffffff);
  18         const uint32_t absHighWordMinusOne = absHighWord - UINT32_C(0x3ff00000);
  19
  20         /* If (1.0 - tiny) <= input < 0x1.0p63: */
  21         if (UINT32_C(0x03f00000) > absHighWordMinusOne)
  22         {
  23                 /* Do an unsigned conversion of the absolute value, then restore the sign. */
  24                 const int unbiasedHeadExponent = absHighWordMinusOne >> 20;
  25
  26                 int64_t result = hibits.x & INT64_C(0x000fffffffffffff); /* mantissa(hi) */
  27                 result |= INT64_C(0x0010000000000000); /* matissa(hi) with implicit bit */
  28                 result <<= 10; /* mantissa(hi) with one zero preceding bit. */
  29
  30                 const int64_t hiNegationMask = ((int64_t)(hibits.x)) >> 63;
  31
  32                 /* If the tail is non-zero, we need to patch in the tail bits. */
  33                 if (0.0 != x.s.lo)
  34                 {
  35                         const doublebits lobits = { .d = x.s.lo };
  36                         int64_t tailMantissa = lobits.x & INT64_C(0x000fffffffffffff);
  37                         tailMantissa |= INT64_C(0x0010000000000000);
  38
  39                         /* At this point we have the mantissa of |tail| */
  40                         /* We need to negate it if head and tail have different signs. */
  41                         const int64_t loNegationMask = ((int64_t)(lobits.x)) >> 63;
  42                         const int64_t negationMask = loNegationMask ^ hiNegationMask;
  43                         tailMantissa = (tailMantissa ^ negationMask) - negationMask;
  44
  45                         /* Now we have the mantissa of tail as a signed 2s-complement integer */
  46
  47                         const int biasedTailExponent = (int)(lobits.x >> 52) & 0x7ff;
  48
  49                         /* Shift the tail mantissa into the right position, accounting for the
  50                          * bias of 10 that we shifted the head mantissa by.
  51                          */
  52                         tailMantissa >>= (unbiasedHeadExponent - (biasedTailExponent - (1023 - 10)));
  53
  54                         result += tailMantissa;
  55                 }
  56
  57                 result >>= (62 - unbiasedHeadExponent);
  58
  59                 /* Restore the sign of the result and return */
  60                 result = (result ^ hiNegationMask) - hiNegationMask;
  61                 return result;
  62
  63         }
  64
  65         /* Edge cases handled here: */
  66
  67         /* |x| < 1, result is zero. */
  68         if (1.0 > crt_fabs(x.s.hi))
  69                 return INT64_C(0);
  70
  71         /* x very close to INT64_MIN, care must be taken to see which side we are on. */
  72         if (x.s.hi == -0x1.0p63) {
  73
  74                 int64_t result = INT64_MIN;
  75
  76                 if (0.0 < x.s.lo)
  77                 {
  78                         /* If the tail is positive, the correct result is something other than INT64_MIN.
  79                          * we'll need to figure out what it is.
  80                          */
  81
  82                         const doublebits lobits = { .d = x.s.lo };
  83                         int64_t tailMantissa = lobits.x & INT64_C(0x000fffffffffffff);
  84                         tailMantissa |= INT64_C(0x0010000000000000);
  85
  86                         /* Now we negate the tailMantissa */
  87                         tailMantissa = (tailMantissa ^ INT64_C(-1)) + INT64_C(1);
  88
  89                         /* And shift it by the appropriate amount */
  90                         const int biasedTailExponent = (int)(lobits.x >> 52) & 0x7ff;
  91                         tailMantissa >>= 1075 - biasedTailExponent;
  92
  93                         result -= tailMantissa;
  94                 }
  95
  96                 return result;
  97         }
  98
  99         /* Signed overflows, infinities, and NaNs */
 100         if (x.s.hi > 0.0)
 101                 return INT64_MAX;
 102         else
 103                 return INT64_MIN;
 104 }