1/*===-- floatdidf.c - Implement __floatdidf -------------------------------===
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 __floatdidf for the compiler_rt library.
11 *
12 *===----------------------------------------------------------------------===
13 */
14
15#include "int_lib.h"
16
17/* Returns: convert a to a double, rounding toward even. */
18
19/* Assumption: double is a IEEE 64 bit floating point type
20 *             di_int is a 64 bit integral type
21 */
22
23/* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */
24
25ARM_EABI_FNALIAS(l2d, floatdidf)
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
32COMPILER_RT_ABI double
33__floatdidf(di_int a)
34{
35	static const double twop52 = 0x1.0p52;
36	static const double twop32 = 0x1.0p32;
37
38	union { int64_t x; double d; } low = { .d = twop52 };
39
40	const double high = (int32_t)(a >> 32) * twop32;
41	low.x |= a & INT64_C(0x00000000ffffffff);
42
43	const double result = (high - twop52) + low.d;
44	return result;
45}
46
47#else
48/* Support for systems that don't have hardware floating-point; there are no flags to
49 * set, and we don't want to code-gen to an unknown soft-float implementation.
50 */
51
52COMPILER_RT_ABI double
53__floatdidf(di_int a)
54{
55    if (a == 0)
56        return 0.0;
57    const unsigned N = sizeof(di_int) * CHAR_BIT;
58    const di_int s = a >> (N-1);
59    a = (a ^ s) - s;
60    int sd = N - __builtin_clzll(a);  /* number of significant digits */
61    int e = sd - 1;             /* exponent */
62    if (sd > DBL_MANT_DIG)
63    {
64        /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
65         *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
66         *                                                12345678901234567890123456
67         *  1 = msb 1 bit
68         *  P = bit DBL_MANT_DIG-1 bits to the right of 1
69         * Q = bit DBL_MANT_DIG bits to the right of 1
70         *  R = "or" of all bits to the right of Q
71        */
72        switch (sd)
73        {
74        case DBL_MANT_DIG + 1:
75            a <<= 1;
76            break;
77        case DBL_MANT_DIG + 2:
78            break;
79        default:
80            a = ((du_int)a >> (sd - (DBL_MANT_DIG+2))) |
81                ((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0);
82        };
83        /* finish: */
84        a |= (a & 4) != 0;  /* Or P into R */
85        ++a;  /* round - this step may add a significant bit */
86        a >>= 2;  /* dump Q and R */
87        /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */
88        if (a & ((du_int)1 << DBL_MANT_DIG))
89        {
90            a >>= 1;
91            ++e;
92        }
93        /* a is now rounded to DBL_MANT_DIG bits */
94    }
95    else
96    {
97        a <<= (DBL_MANT_DIG - sd);
98        /* a is now rounded to DBL_MANT_DIG bits */
99    }
100    double_bits fb;
101    fb.u.high = ((su_int)s & 0x80000000) |        /* sign */
102                ((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