floatdisf.c revision 222656 
1/*===-- floatdisf.c - Implement __floatdisf -------------------------------===
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 __floatdisf 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 *             di_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(l2f, floatdisf);
29
30COMPILER_RT_ABI float
31__floatdisf(di_int a)
32{
33    if (a == 0)
34        return 0.0F;
35    const unsigned N = sizeof(di_int) * CHAR_BIT;
36    const di_int s = a >> (N-1);
37    a = (a ^ s) - s;
38    int sd = N - __builtin_clzll(a);  /* number of significant digits */
39    int e = sd - 1;             /* exponent */
40    if (sd > FLT_MANT_DIG)
41    {
42        /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
43         *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
44         *                                                12345678901234567890123456
45         *  1 = msb 1 bit
46         *  P = bit FLT_MANT_DIG-1 bits to the right of 1
47         *  Q = bit FLT_MANT_DIG bits to the right of 1
48         *  R = "or" of all bits to the right of Q
49         */
50        switch (sd)
51        {
52        case FLT_MANT_DIG + 1:
53            a <<= 1;
54            break;
55        case FLT_MANT_DIG + 2:
56            break;
57        default:
58            a = ((du_int)a >> (sd - (FLT_MANT_DIG+2))) |
59                ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
60        };
61        /* finish: */
62        a |= (a & 4) != 0;  /* Or P into R */
63        ++a;  /* round - this step may add a significant bit */
64        a >>= 2;  /* dump Q and R */
65        /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
66        if (a & ((du_int)1 << FLT_MANT_DIG))
67        {
68            a >>= 1;
69            ++e;
70        }
71        /* a is now rounded to FLT_MANT_DIG bits */
72    }
73    else
74    {
75        a <<= (FLT_MANT_DIG - sd);
76        /* a is now rounded to FLT_MANT_DIG bits */
77    }
78    float_bits fb;
79    fb.u = ((su_int)s & 0x80000000) |  /* sign */
80           ((e + 127) << 23)       |  /* exponent */
81           ((su_int)a & 0x007FFFFF);   /* mantissa */
82    return fb.f;
83}
84