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 #if __x86_64
16
17 #include "int_lib.h"
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 si_int __clzti2(ti_int a);
28
29 double
__floattidf(ti_int a)30 __floattidf(ti_int a)
31 {
32 if (a == 0)
33 return 0.0;
34 const unsigned N = sizeof(ti_int) * CHAR_BIT;
35 const ti_int s = a >> (N-1);
36 a = (a ^ s) - s;
37 int sd = N - __clzti2(a); /* number of significant digits */
38 int e = sd - 1; /* exponent */
39 if (sd > DBL_MANT_DIG)
40 {
41 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
42 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
43 * 12345678901234567890123456
44 * 1 = msb 1 bit
45 * P = bit DBL_MANT_DIG-1 bits to the right of 1
46 * Q = bit DBL_MANT_DIG bits to the right of 1
47 * R = "or" of all bits to the right of Q
48 */
49 switch (sd)
50 {
51 case DBL_MANT_DIG + 1:
52 a <<= 1;
53 break;
54 case DBL_MANT_DIG + 2:
55 break;
56 default:
57 a = ((tu_int)a >> (sd - (DBL_MANT_DIG+2))) |
58 ((a & ((tu_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0);
59 };
60 /* finish: */
61 a |= (a & 4) != 0; /* Or P into R */
62 ++a; /* round - this step may add a significant bit */
63 a >>= 2; /* dump Q and R */
64 /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */
65 if (a & ((tu_int)1 << DBL_MANT_DIG))
66 {
67 a >>= 1;
68 ++e;
69 }
70 /* a is now rounded to DBL_MANT_DIG bits */
71 }
72 else
73 {
74 a <<= (DBL_MANT_DIG - sd);
75 /* a is now rounded to DBL_MANT_DIG bits */
76 }
77 double_bits fb;
78 fb.u.s.high = ((su_int)s & 0x80000000) | /* sign */
79 ((e + 1023) << 20) | /* exponent */
80 ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */
81 fb.u.s.low = (su_int)a; /* mantissa-low */
82 return fb.f;
83 }
84
85 #endif
86