floatundisf.c revision 222656 
1/*===-- floatundisf.c - Implement __floatundisf ---------------------------===
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 __floatundisf for the compiler_rt library.
11 *
12 *===----------------------------------------------------------------------===
13 */
14
15#include "abi.h"
16#include <float.h>
17
18/* Returns: convert a to a float, rounding toward even. */
19
20/* Assumption: float is a IEEE 32 bit floating point type
21 *            du_int is a 64 bit integral type
22 */
23
24/* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */
25
26#include "int_lib.h"
27
28ARM_EABI_FNALIAS(ul2f, floatundisf);
29
30COMPILER_RT_ABI float
31__floatundisf(du_int a)
32{
33    if (a == 0)
34        return 0.0F;
35    const unsigned N = sizeof(du_int) * CHAR_BIT;
36    int sd = N - __builtin_clzll(a);  /* number of significant digits */
37    int e = sd - 1;             /* 8 exponent */
38    if (sd > FLT_MANT_DIG)
39    {
40        /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
41         *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
42         *                                                12345678901234567890123456
43         *  1 = msb 1 bit
44         *  P = bit FLT_MANT_DIG-1 bits to the right of 1
45         *  Q = bit FLT_MANT_DIG bits to the right of 1
46         *  R = "or" of all bits to the right of Q
47         */
48        switch (sd)
49        {
50        case FLT_MANT_DIG + 1:
51            a <<= 1;
52            break;
53        case FLT_MANT_DIG + 2:
54            break;
55        default:
56            a = (a >> (sd - (FLT_MANT_DIG+2))) |
57                ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
58        };
59        /* finish: */
60        a |= (a & 4) != 0;  /* Or P into R */
61        ++a;  /* round - this step may add a significant bit */
62        a >>= 2;  /* dump Q and R */
63        /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
64        if (a & ((du_int)1 << FLT_MANT_DIG))
65        {
66            a >>= 1;
67            ++e;
68        }
69        /* a is now rounded to FLT_MANT_DIG bits */
70    }
71    else
72    {
73        a <<= (FLT_MANT_DIG - sd);
74        /* a is now rounded to FLT_MANT_DIG bits */
75    }
76    float_bits fb;
77    fb.u = ((e + 127) << 23)       |  /* exponent */
78           ((su_int)a & 0x007FFFFF);  /* mantissa */
79    return fb.f;
80}
81