compiler-rt/lib/builtins/fixxfti.c

   1 //===-- fixxfti.c - Implement __fixxfti -----------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements __fixxfti for the compiler_rt library.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "int_lib.h"
  14
  15 #ifdef CRT_HAS_128BIT
  16
  17 // Returns: convert a to a signed long long, rounding toward zero.
  18
  19 // Assumption: long double is an intel 80 bit floating point type padded with 6
  20 // bytes ti_int is a 128 bit integral type value in long double is representable
  21 // in ti_int
  22
  23 // gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee
  24 // eeee | 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm
  25 // mmmm mmmm mmmm
  26
  27 COMPILER_RT_ABI ti_int __fixxfti(long double a) {
  28   const ti_int ti_max = (ti_int)((~(tu_int)0) / 2);
  29   const ti_int ti_min = -ti_max - 1;
  30   long_double_bits fb;
  31   fb.f = a;
  32   int e = (fb.u.high.s.low & 0x00007FFF) - 16383;
  33   if (e < 0)
  34     return 0;
  35   ti_int s = -(si_int)((fb.u.high.s.low & 0x00008000) >> 15);
  36   ti_int r = fb.u.low.all;
  37   if ((unsigned)e >= sizeof(ti_int) * CHAR_BIT)
  38     return a > 0 ? ti_max : ti_min;
  39   if (e > 63)
  40     r <<= (e - 63);
  41   else
  42     r >>= (63 - e);
  43   return (r ^ s) - s;
  44 }
  45
  46 #endif // CRT_HAS_128BIT