1/* ===-- floatuntixf.c - Implement __floatuntixf ---------------------------===
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 __floatuntixf for the compiler_rt library.
11 *
12 * ===----------------------------------------------------------------------===
13 */
14
15#include "int_lib.h"
16
17#ifdef CRT_HAS_128BIT
18
19/* Returns: convert a to a long double, rounding toward even. */
20
21/* Assumption: long double is a IEEE 80 bit floating point type padded to 128 bits
22 *             tu_int is a 128 bit integral type
23 */
24
25/* gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee eeee |
26 * 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm
27 */
28
29COMPILER_RT_ABI long double
30__floatuntixf(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 > LDBL_MANT_DIG)
38    {
39        /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
40         *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
41         *                                                12345678901234567890123456
42         *  1 = msb 1 bit
43         *  P = bit LDBL_MANT_DIG-1 bits to the right of 1
44         *  Q = bit LDBL_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 LDBL_MANT_DIG + 1:
50            a <<= 1;
51            break;
52        case LDBL_MANT_DIG + 2:
53            break;
54        default:
55            a = (a >> (sd - (LDBL_MANT_DIG+2))) |
56                ((a & ((tu_int)(-1) >> ((N + LDBL_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 LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits */
63        if (a & ((tu_int)1 << LDBL_MANT_DIG))
64        {
65            a >>= 1;
66            ++e;
67        }
68        /* a is now rounded to LDBL_MANT_DIG bits */
69    }
70    else
71    {
72        a <<= (LDBL_MANT_DIG - sd);
73        /* a is now rounded to LDBL_MANT_DIG bits */
74    }
75    long_double_bits fb;
76    fb.u.high.s.low = (e + 16383);                  /* exponent */
77    fb.u.low.all = (du_int)a;                     /* mantissa */
78    return fb.f;
79}
80
81#endif
82