1 /* ===-- floattidf.c - Implement __floattidf -------------------------------===
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 __floattidf 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 double, rounding toward even.*/
20
21 /* Assumption: double is a IEEE 64 bit floating point type
22 * ti_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
27 COMPILER_RT_ABI double
__floattidf(ti_int a)28 __floattidf(ti_int a)
29 {
30 if (a == 0)
31 return 0.0;
32 const unsigned N = sizeof(ti_int) * CHAR_BIT;
33 const ti_int s = a >> (N-1);
34 a = (a ^ s) - s;
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 = ((tu_int)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 = ((su_int)s & 0x80000000) | /* sign */
77 ((e + 1023) << 20) | /* exponent */
78 ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */
79 fb.u.s.low = (su_int)a; /* mantissa-low */
80 return fb.f;
81 }
82
83 #endif /* CRT_HAS_128BIT */
84