1/* ===-- floatuntidf.c - Implement __floatuntidf ---------------------------===
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 __floatuntidf for the compiler_rt library.
11 *
12 * ===----------------------------------------------------------------------===
13 */
14
15#include "int_lib.h"
16
17#if __x86_64
18
19/* Returns: convert a to a double, rounding toward even. */
20
21/* Assumption: double is a IEEE 64 bit floating point type
22 *             tu_int is a 128 bit integral type
23 */
24
25/* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */
26
27si_int __clzti2(ti_int a);
28
29double
30__floatuntidf(tu_int a)
31{
32    if (a == 0)
33        return 0.0;
34    const unsigned N = sizeof(tu_int) * CHAR_BIT;
35    int sd = N - __clzti2(a);  /* number of significant digits */
36    int e = sd - 1;             /* exponent */
37    if (sd > DBL_MANT_DIG)
38    {
39        /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
40         *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
41         *                                                12345678901234567890123456
42         *  1 = msb 1 bit
43         *  P = bit DBL_MANT_DIG-1 bits to the right of 1
44         *  Q = bit DBL_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 DBL_MANT_DIG + 1:
50            a <<= 1;
51            break;
52        case DBL_MANT_DIG + 2:
53            break;
54        default:
55            a = (a >> (sd - (DBL_MANT_DIG+2))) |
56                ((a & ((tu_int)(-1) >> ((N + DBL_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 DBL_MANT_DIG or DBL_MANT_DIG+1 bits */
63        if (a & ((tu_int)1 << DBL_MANT_DIG))
64        {
65            a >>= 1;
66            ++e;
67        }
68        /* a is now rounded to DBL_MANT_DIG bits */
69    }
70    else
71    {
72        a <<= (DBL_MANT_DIG - sd);
73        /* a is now rounded to DBL_MANT_DIG bits */
74    }
75    double_bits fb;
76    fb.u.s.high = ((e + 1023) << 20)      |        /* exponent */
77                ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */
78    fb.u.s.low = (su_int)a;                         /* mantissa-low */
79    return fb.f;
80}
81
82#endif
83