floatsisf.c revision 214152 
1//===-- lib/floatsisf.c - integer -> single-precision conversion --*- C -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements integer to single-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 SINGLE_PRECISION
17#include "fp_lib.h"
18
19fp_t __floatsisf(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)
25        return fromRep(0);
26
27    // All other cases begin by extracting the sign and absolute value of a
28    rep_t sign = 0;
29    if (a < 0) {
30        sign = signBit;
31        a = -a;
32    }
33
34    // Exponent of (fp_t)a is the width of abs(a).
35    const int exponent = (aWidth - 1) - __builtin_clz(a);
36    rep_t result;
37
38    // Shift a into the significand field, rounding if it is a right-shift
39    if (exponent <= significandBits) {
40        const int shift = significandBits - exponent;
41        result = (rep_t)a << shift ^ implicitBit;
42    } else {
43        const int shift = exponent - significandBits;
44        result = (rep_t)a >> shift ^ implicitBit;
45        rep_t round = (rep_t)a << (typeWidth - shift);
46        if (round > signBit) result++;
47        if (round == signBit) result += result & 1;
48    }
49
50    // Insert the exponent
51    result += (rep_t)(exponent + exponentBias) << significandBits;
52    // Insert the sign bit and return
53    return fromRep(result | sign);
54}
55