1276789Sdim/* ===-- floatuntisf.c - Implement __floatuntisf ---------------------------===
2276789Sdim *
3276789Sdim *                     The LLVM Compiler Infrastructure
4276789Sdim *
5276789Sdim * This file is dual licensed under the MIT and the University of Illinois Open
6276789Sdim * Source Licenses. See LICENSE.TXT for details.
7276789Sdim *
8276789Sdim * ===----------------------------------------------------------------------===
9276789Sdim *
10276789Sdim * This file implements __floatuntisf for the compiler_rt library.
11276789Sdim *
12276789Sdim * ===----------------------------------------------------------------------===
13276789Sdim */
14276789Sdim
15276789Sdim#include "int_lib.h"
16276789Sdim
17276789Sdim#ifdef CRT_HAS_128BIT
18276789Sdim
19276789Sdim/* Returns: convert a to a float, rounding toward even. */
20276789Sdim
21276789Sdim/* Assumption: float is a IEEE 32 bit floating point type
22276789Sdim *             tu_int is a 128 bit integral type
23276789Sdim */
24276789Sdim
25276789Sdim/* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */
26276789Sdim
27276789SdimCOMPILER_RT_ABI float
28276789Sdim__floatuntisf(tu_int a)
29276789Sdim{
30276789Sdim    if (a == 0)
31276789Sdim        return 0.0F;
32276789Sdim    const unsigned N = sizeof(tu_int) * CHAR_BIT;
33276789Sdim    int sd = N - __clzti2(a);  /* number of significant digits */
34276789Sdim    int e = sd - 1;             /* exponent */
35276789Sdim    if (sd > FLT_MANT_DIG)
36276789Sdim    {
37276789Sdim        /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
38276789Sdim         *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
39276789Sdim         *                                                12345678901234567890123456
40276789Sdim         *  1 = msb 1 bit
41276789Sdim         *  P = bit FLT_MANT_DIG-1 bits to the right of 1
42276789Sdim         *  Q = bit FLT_MANT_DIG bits to the right of 1
43276789Sdim         *  R = "or" of all bits to the right of Q
44276789Sdim	 */
45276789Sdim        switch (sd)
46276789Sdim        {
47276789Sdim        case FLT_MANT_DIG + 1:
48276789Sdim            a <<= 1;
49276789Sdim            break;
50276789Sdim        case FLT_MANT_DIG + 2:
51276789Sdim            break;
52276789Sdim        default:
53276789Sdim            a = (a >> (sd - (FLT_MANT_DIG+2))) |
54276789Sdim                ((a & ((tu_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
55276789Sdim        };
56276789Sdim        /* finish: */
57276789Sdim        a |= (a & 4) != 0;  /* Or P into R */
58276789Sdim        ++a;  /* round - this step may add a significant bit */
59276789Sdim        a >>= 2;  /* dump Q and R */
60276789Sdim        /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
61276789Sdim        if (a & ((tu_int)1 << FLT_MANT_DIG))
62276789Sdim        {
63276789Sdim            a >>= 1;
64276789Sdim            ++e;
65276789Sdim        }
66276789Sdim        /* a is now rounded to FLT_MANT_DIG bits */
67276789Sdim    }
68276789Sdim    else
69276789Sdim    {
70276789Sdim        a <<= (FLT_MANT_DIG - sd);
71276789Sdim        /* a is now rounded to FLT_MANT_DIG bits */
72276789Sdim    }
73276789Sdim    float_bits fb;
74276789Sdim    fb.u = ((e + 127) << 23)       |  /* exponent */
75276789Sdim           ((su_int)a & 0x007FFFFF);  /* mantissa */
76276789Sdim    return fb.f;
77276789Sdim}
78276789Sdim
79276789Sdim#endif /* CRT_HAS_128BIT */
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