lib/builtins/floatunsidf.c

   1 //===-- lib/floatunsidf.c - uint -> 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 unsigned 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(ui2d, floatunsidf)
  22
  23 COMPILER_RT_ABI fp_t
  24 __floatunsidf(unsigned 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) return fromRep(0);
  30
  31     // Exponent of (fp_t)a is the width of abs(a).
  32     const int exponent = (aWidth - 1) - __builtin_clz(a);
  33     rep_t result;
  34
  35     // Shift a into the significand field and clear the implicit bit.
  36     const int shift = significandBits - exponent;
  37     result = (rep_t)a << shift ^ implicitBit;
  38
  39     // Insert the exponent
  40     result += (rep_t)(exponent + exponentBias) << significandBits;
  41     return fromRep(result);
  42 }