floatundisf.c revision 327952 
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/* Returns: convert a to a float, rounding toward even. */
16
17/* Assumption: float is a IEEE 32 bit floating point type
18 *            du_int is a 64 bit integral type
19 */
20
21/* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */
22
23#include "int_lib.h"
24
25COMPILER_RT_ABI float
26__floatundisf(du_int a)
27{
28    if (a == 0)
29        return 0.0F;
30    const unsigned N = sizeof(du_int) * CHAR_BIT;
31    int sd = N - __builtin_clzll(a);  /* number of significant digits */
32    int e = sd - 1;             /* 8 exponent */
33    if (sd > FLT_MANT_DIG)
34    {
35        /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
36         *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
37         *                                                12345678901234567890123456
38         *  1 = msb 1 bit
39         *  P = bit FLT_MANT_DIG-1 bits to the right of 1
40         *  Q = bit FLT_MANT_DIG bits to the right of 1
41         *  R = "or" of all bits to the right of Q
42         */
43        switch (sd)
44        {
45        case FLT_MANT_DIG + 1:
46            a <<= 1;
47            break;
48        case FLT_MANT_DIG + 2:
49            break;
50        default:
51            a = (a >> (sd - (FLT_MANT_DIG+2))) |
52                ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
53        };
54        /* finish: */
55        a |= (a & 4) != 0;  /* Or P into R */
56        ++a;  /* round - this step may add a significant bit */
57        a >>= 2;  /* dump Q and R */
58        /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
59        if (a & ((du_int)1 << FLT_MANT_DIG))
60        {
61            a >>= 1;
62            ++e;
63        }
64        /* a is now rounded to FLT_MANT_DIG bits */
65    }
66    else
67    {
68        a <<= (FLT_MANT_DIG - sd);
69        /* a is now rounded to FLT_MANT_DIG bits */
70    }
71    float_bits fb;
72    fb.u = ((e + 127) << 23)       |  /* exponent */
73           ((su_int)a & 0x007FFFFF);  /* mantissa */
74    return fb.f;
75}
76
77#if defined(__ARM_EABI__)
78#if defined(COMPILER_RT_ARMHF_TARGET)
79AEABI_RTABI float __aeabi_ul2f(du_int a) {
80  return __floatundisf(a);
81}
82#else
83AEABI_RTABI float __aeabi_ul2f(du_int a) COMPILER_RT_ALIAS(__floatundisf);
84#endif
85#endif
86