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