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

   1 //===-- lib/floatsidf.c - integer -> double-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 double-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 DOUBLE_PRECISION
  17 #include "fp_lib.h"
  18
  19 #include "int_lib.h"
  20
  21 ARM_EABI_FNALIAS(i2d, floatsidf)
  22
  23 COMPILER_RT_ABI fp_t
  24 __floatsidf(int a) {
  25
  26     const int aWidth = sizeof a * CHAR_BIT;
  27
  28     // Handle zero as a special case to protect clz
  29     if (a == 0)
  30         return fromRep(0);
  31
  32     // All other cases begin by extracting the sign and absolute value of a
  33     rep_t sign = 0;
  34     unsigned aAbs = (unsigned)a;
  35     if (a < 0) {
  36         sign = signBit;
  37         aAbs = ~(unsigned)a + 1U;
  38     }
  39
  40     // Exponent of (fp_t)a is the width of abs(a).
  41     const int exponent = (aWidth - 1) - __builtin_clz(aAbs);
  42     rep_t result;
  43
  44     // Shift a into the significand field and clear the implicit bit.
  45     const int shift = significandBits - exponent;
  46     result = (rep_t)aAbs << shift ^ implicitBit;
  47
  48     // Insert the exponent
  49     result += (rep_t)(exponent + exponentBias) << significandBits;
  50     // Insert the sign bit and return
  51     return fromRep(result | sign);
  52 }