floattisf.c revision 2d1fdb26e458c4ddc04155c1d421bced3ba90cd0 
1/* ===-- floattisf.c - Implement __floattisf -------------------------------===
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 __floattisf for the compiler_rt library.
11 *
12 * ===----------------------------------------------------------------------===
13 */
14
15#include "int_lib.h"
16
17#ifdef CRT_HAS_128BIT
18
19/* Returns: convert a to a float, rounding toward even. */
20
21/* Assumption: float is a IEEE 32 bit floating point type
22 *             ti_int is a 128 bit integral type
23 */
24
25/* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */
26
27COMPILER_RT_ABI float
28__floattisf(ti_int a)
29{
30    if (a == 0)
31        return 0.0F;
32    const unsigned N = sizeof(ti_int) * CHAR_BIT;
33    const ti_int s = a >> (N-1);
34    a = (a ^ s) - s;
35    int sd = N - __clzti2(a);  /* number of significant digits */
36    int e = sd - 1;             /* exponent */
37    if (sd > FLT_MANT_DIG)
38    {
39        /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
40        * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
41        *                                                12345678901234567890123456
42        *  1 = msb 1 bit
43        *  P = bit FLT_MANT_DIG-1 bits to the right of 1
44        *  Q = bit FLT_MANT_DIG bits to the right of 1
45        *  R = "or" of all bits to the right of Q
46        */
47        switch (sd)
48        {
49        case FLT_MANT_DIG + 1:
50            a <<= 1;
51            break;
52        case FLT_MANT_DIG + 2:
53            break;
54        default:
55            a = ((tu_int)a >> (sd - (FLT_MANT_DIG+2))) |
56                ((a & ((tu_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
57        };
58        /* finish: */
59        a |= (a & 4) != 0;  /* Or P into R */
60        ++a;  /* round - this step may add a significant bit */
61        a >>= 2;  /* dump Q and R */
62        /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
63        if (a & ((tu_int)1 << FLT_MANT_DIG))
64        {
65            a >>= 1;
66            ++e;
67        }
68        /* a is now rounded to FLT_MANT_DIG bits */
69    }
70    else
71    {
72        a <<= (FLT_MANT_DIG - sd);
73        /* a is now rounded to FLT_MANT_DIG bits */
74    }
75    float_bits fb;
76    fb.u = ((su_int)s & 0x80000000) |  /* sign */
77           ((e + 127) << 23)       |  /* exponent */
78           ((su_int)a & 0x007FFFFF);   /* mantissa */
79    return fb.f;
80}
81
82#endif /* CRT_HAS_128BIT */
83