1/* ===-- floatundidf.c - Implement __floatundidf ---------------------------===
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 __floatundidf for the compiler_rt library.
11 *
12 * ===----------------------------------------------------------------------===
13 */
14
15/* Returns: convert a to a double, rounding toward even. */
16
17/* Assumption: double is a IEEE 64 bit floating point type
18 *             du_int is a 64 bit integral type
19 */
20
21/* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */
22
23#include "int_lib.h"
24
25ARM_EABI_FNALIAS(ul2d, floatundidf)
26
27#ifndef __SOFT_FP__
28/* Support for systems that have hardware floating-point; we'll set the inexact flag
29 * as a side-effect of this computation.
30 */
31
32
33COMPILER_RT_ABI double
34__floatundidf(du_int a)
35{
36	static const double twop52 = 0x1.0p52;
37	static const double twop84 = 0x1.0p84;
38	static const double twop84_plus_twop52 = 0x1.00000001p84;
39
40	union { uint64_t x; double d; } high = { .d = twop84 };
41	union { uint64_t x; double d; } low = { .d = twop52 };
42
43	high.x |= a >> 32;
44	low.x |= a & UINT64_C(0x00000000ffffffff);
45
46	const double result = (high.d - twop84_plus_twop52) + low.d;
47	return result;
48}
49
50#else
51/* Support for systems that don't have hardware floating-point; there are no flags to
52 * set, and we don't want to code-gen to an unknown soft-float implementation.
53 */
54
55COMPILER_RT_ABI double
56__floatundidf(du_int a)
57{
58    if (a == 0)
59        return 0.0;
60    const unsigned N = sizeof(du_int) * CHAR_BIT;
61    int sd = N - __builtin_clzll(a);  /* number of significant digits */
62    int e = sd - 1;             /* exponent */
63    if (sd > DBL_MANT_DIG)
64    {
65        /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
66         *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
67         *                                                12345678901234567890123456
68         *  1 = msb 1 bit
69         *  P = bit DBL_MANT_DIG-1 bits to the right of 1
70         *  Q = bit DBL_MANT_DIG bits to the right of 1
71         *  R = "or" of all bits to the right of Q
72         */
73        switch (sd)
74        {
75        case DBL_MANT_DIG + 1:
76            a <<= 1;
77            break;
78        case DBL_MANT_DIG + 2:
79            break;
80        default:
81            a = (a >> (sd - (DBL_MANT_DIG+2))) |
82                ((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0);
83        };
84        /* finish: */
85        a |= (a & 4) != 0;  /* Or P into R */
86        ++a;  /* round - this step may add a significant bit */
87        a >>= 2;  /* dump Q and R */
88        /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */
89        if (a & ((du_int)1 << DBL_MANT_DIG))
90        {
91            a >>= 1;
92            ++e;
93        }
94        /* a is now rounded to DBL_MANT_DIG bits */
95    }
96    else
97    {
98        a <<= (DBL_MANT_DIG - sd);
99        /* a is now rounded to DBL_MANT_DIG bits */
100    }
101    double_bits fb;
102    fb.u.high = ((e + 1023) << 20)      |        /* exponent */
103                ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */
104    fb.u.low = (su_int)a;                         /* mantissa-low  */
105    return fb.f;
106}
107#endif
108