floatdisf.c revision 1.3 
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/* Returns: convert a to a float, rounding toward even.*/
16
17/* Assumption: float is a IEEE 32 bit floating point type
18 *             di_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__floatdisf(di_int a)
27{
28    if (a == 0)
29        return 0.0F;
30    const unsigned N = sizeof(di_int) * CHAR_BIT;
31    const di_int s = a >> (N-1);
32    a = (a ^ s) - s;
33    int sd = N - __builtin_clzll(a);  /* number of significant digits */
34    int e = sd - 1;             /* exponent */
35    if (sd > FLT_MANT_DIG)
36    {
37        /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
38         *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
39         *                                                12345678901234567890123456
40         *  1 = msb 1 bit
41         *  P = bit FLT_MANT_DIG-1 bits to the right of 1
42         *  Q = bit FLT_MANT_DIG bits to the right of 1
43         *  R = "or" of all bits to the right of Q
44         */
45        switch (sd)
46        {
47        case FLT_MANT_DIG + 1:
48            a <<= 1;
49            break;
50        case FLT_MANT_DIG + 2:
51            break;
52        default:
53            a = ((du_int)a >> (sd - (FLT_MANT_DIG+2))) |
54                ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
55        };
56        /* finish: */
57        a |= (a & 4) != 0;  /* Or P into R */
58        ++a;  /* round - this step may add a significant bit */
59        a >>= 2;  /* dump Q and R */
60        /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
61        if (a & ((du_int)1 << FLT_MANT_DIG))
62        {
63            a >>= 1;
64            ++e;
65        }
66        /* a is now rounded to FLT_MANT_DIG bits */
67    }
68    else
69    {
70        a <<= (FLT_MANT_DIG - sd);
71        /* a is now rounded to FLT_MANT_DIG bits */
72    }
73    float_bits fb;
74    fb.u = ((su_int)s & 0x80000000) |  /* sign */
75           ((e + 127) << 23)       |  /* exponent */
76           ((su_int)a & 0x007FFFFF);   /* mantissa */
77    return fb.f;
78}
79
80#if defined(__ARM_EABI__)
81#if defined(COMPILER_RT_ARMHF_TARGET)
82AEABI_RTABI float __aeabi_l2f(di_int a) {
83  return __floatdisf(a);
84}
85#else
86AEABI_RTABI float __aeabi_l2f(di_int a) COMPILER_RT_ALIAS(__floatdisf);
87#endif
88#endif
89