src/compiler-rt/lib/builtins/floatsitf.c

   1 //===-- lib/floatsitf.c - integer -> quad-precision conversion ----*- C -*-===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is dual licensed under the MIT and the University of Illinois Open
   6 // Source Licenses. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements integer to quad-precision conversion for the
  11 // compiler-rt library in the IEEE-754 default round-to-nearest, ties-to-even
  12 // mode.
  13 //
  14 //===----------------------------------------------------------------------===//
  15
  16 #define QUAD_PRECISION
  17 #include "fp_lib.h"
  18
  19 #if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
  20 COMPILER_RT_ABI fp_t __floatsitf(int a) {
  21
  22     const int aWidth = sizeof a * CHAR_BIT;
  23
  24     // Handle zero as a special case to protect clz
  25     if (a == 0)
  26         return fromRep(0);
  27
  28     // All other cases begin by extracting the sign and absolute value of a
  29     rep_t sign = 0;
  30     unsigned aAbs = (unsigned)a;
  31     if (a < 0) {
  32         sign = signBit;
  33         aAbs = ~(unsigned)a + 1U;
  34     }
  35
  36     // Exponent of (fp_t)a is the width of abs(a).
  37     const int exponent = (aWidth - 1) - __builtin_clz(aAbs);
  38     rep_t result;
  39
  40     // Shift a into the significand field and clear the implicit bit.
  41     const int shift = significandBits - exponent;
  42     result = (rep_t)aAbs << shift ^ implicitBit;
  43
  44     // Insert the exponent
  45     result += (rep_t)(exponent + exponentBias) << significandBits;
  46     // Insert the sign bit and return
  47     return fromRep(result | sign);
  48 }
  49
  50 #endif