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