compiler-rt/lib/builtins/floatdixf.c

   1 //===-- floatdixf.c - Implement __floatdixf -------------------------------===//
   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 __floatdixf for the compiler_rt library.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #if !_ARCH_PPC
  14
  15 #include "int_lib.h"
  16
  17 // Returns: convert a to a long double, rounding toward even.
  18
  19 // Assumption: long double is a IEEE 80 bit floating point type padded to 128
  20 // bits di_int is a 64 bit integral type
  21
  22 // gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee
  23 // eeee | 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm
  24 // mmmm mmmm mmmm
  25
  26 COMPILER_RT_ABI long double __floatdixf(di_int a) {
  27   if (a == 0)
  28     return 0.0;
  29   const unsigned N = sizeof(di_int) * CHAR_BIT;
  30   const di_int s = a >> (N - 1);
  31   a = (a ^ s) - s;
  32   int clz = __builtin_clzll(a);
  33   int e = (N - 1) - clz; // exponent
  34   long_double_bits fb;
  35   fb.u.high.s.low = ((su_int)s & 0x00008000) | // sign
  36                     (e + 16383);               // exponent
  37   fb.u.low.all = a << clz;                     // mantissa
  38   return fb.f;
  39 }
  40
  41 #endif // !_ARCH_PPC