floatunsidf.c revision 9ad441ffec97db647fee3725b3424284fb913e14 
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
19fp_t __floatunsidf(unsigned int a) {
20
21    const int aWidth = sizeof a * CHAR_BIT;
22
23    // Handle zero as a special case to protect clz
24    if (a == 0) return fromRep(0);
25
26    // Exponent of (fp_t)a is the width of abs(a).
27    const int exponent = (aWidth - 1) - __builtin_clz(a);
28    rep_t result;
29
30    // Shift a into the significand field and clear the implicit bit.
31    const int shift = significandBits - exponent;
32    result = (rep_t)a << shift ^ implicitBit;
33
34    // Insert the exponent
35    result += (rep_t)(exponent + exponentBias) << significandBits;
36    return fromRep(result);
37}
38