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
25#ifndef __SOFT_FP__
26/* Support for systems that have hardware floating-point; we'll set the inexact flag
27 * as a side-effect of this computation.
28 */
29
30COMPILER_RT_ABI double
31__floatdidf(di_int a)
32{
33	static const double twop52 = 4503599627370496.0; // 0x1.0p52
34	static const double twop32 = 4294967296.0; // 0x1.0p32
35
36	union { int64_t x; double d; } low = { .d = twop52 };
37
38	const double high = (int32_t)(a >> 32) * twop32;
39	low.x |= a & INT64_C(0x00000000ffffffff);
40
41	const double result = (high - twop52) + low.d;
42	return result;
43}
44
45#else
46/* Support for systems that don't have hardware floating-point; there are no flags to
47 * set, and we don't want to code-gen to an unknown soft-float implementation.
48 */
49
50COMPILER_RT_ABI double
51__floatdidf(di_int a)
52{
53    if (a == 0)
54        return 0.0;
55    const unsigned N = sizeof(di_int) * CHAR_BIT;
56    const di_int s = a >> (N-1);
57    a = (a ^ s) - s;
58    int sd = N - __builtin_clzll(a);  /* number of significant digits */
59    int e = sd - 1;             /* exponent */
60    if (sd > DBL_MANT_DIG)
61    {
62        /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
63         *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
64         *                                                12345678901234567890123456
65         *  1 = msb 1 bit
66         *  P = bit DBL_MANT_DIG-1 bits to the right of 1
67         * Q = bit DBL_MANT_DIG bits to the right of 1
68         *  R = "or" of all bits to the right of Q
69        */
70        switch (sd)
71        {
72        case DBL_MANT_DIG + 1:
73            a <<= 1;
74            break;
75        case DBL_MANT_DIG + 2:
76            break;
77        default:
78            a = ((du_int)a >> (sd - (DBL_MANT_DIG+2))) |
79                ((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0);
80        };
81        /* finish: */
82        a |= (a & 4) != 0;  /* Or P into R */
83        ++a;  /* round - this step may add a significant bit */
84        a >>= 2;  /* dump Q and R */
85        /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */
86        if (a & ((du_int)1 << DBL_MANT_DIG))
87        {
88            a >>= 1;
89            ++e;
90        }
91        /* a is now rounded to DBL_MANT_DIG bits */
92    }
93    else
94    {
95        a <<= (DBL_MANT_DIG - sd);
96        /* a is now rounded to DBL_MANT_DIG bits */
97    }
98    double_bits fb;
99    fb.u.s.high = ((su_int)s & 0x80000000) |        /* sign */
100                ((e + 1023) << 20)      |        /* exponent */
101                ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */
102    fb.u.s.low = (su_int)a;                         /* mantissa-low */
103    return fb.f;
104}
105#endif
106
107#if defined(__ARM_EABI__)
108#if defined(COMPILER_RT_ARMHF_TARGET)
109AEABI_RTABI double __aeabi_l2d(di_int a) {
110  return __floatdidf(a);
111}
112#else
113AEABI_RTABI double __aeabi_l2d(di_int a) COMPILER_RT_ALIAS(__floatdidf);
114#endif
115#endif
116