1 /* ===-- floattidf.c - Implement __floattidf -------------------------------===
2 *
3 * The LLVM Compiler Infrastructure
4 *
5 * This file is distributed under the University of Illinois Open Source
6 * License. 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 #include <float.h>
19
20 /* Returns: convert a to a double, rounding toward even.*/
21
22 /* Assumption: double is a IEEE 64 bit floating point type
23 * ti_int is a 128 bit integral type
24 */
25
26 /* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */
27
28 si_int __clzti2(ti_int a);
29
30 double
__floattidf(ti_int a)31 __floattidf(ti_int a)
32 {
33 if (a == 0)
34 return 0.0;
35 const unsigned N = sizeof(ti_int) * CHAR_BIT;
36 const ti_int s = a >> (N-1);
37 a = (a ^ s) - s;
38 int sd = N - __clzti2(a); /* number of significant digits */
39 int e = sd - 1; /* exponent */
40 if (sd > DBL_MANT_DIG)
41 {
42 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
43 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
44 * 12345678901234567890123456
45 * 1 = msb 1 bit
46 * P = bit DBL_MANT_DIG-1 bits to the right of 1
47 * Q = bit DBL_MANT_DIG bits to the right of 1
48 * R = "or" of all bits to the right of Q
49 */
50 switch (sd)
51 {
52 case DBL_MANT_DIG + 1:
53 a <<= 1;
54 break;
55 case DBL_MANT_DIG + 2:
56 break;
57 default:
58 a = ((tu_int)a >> (sd - (DBL_MANT_DIG+2))) |
59 ((a & ((tu_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0);
60 };
61 /* finish: */
62 a |= (a & 4) != 0; /* Or P into R */
63 ++a; /* round - this step may add a significant bit */
64 a >>= 2; /* dump Q and R */
65 /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */
66 if (a & ((tu_int)1 << DBL_MANT_DIG))
67 {
68 a >>= 1;
69 ++e;
70 }
71 /* a is now rounded to DBL_MANT_DIG bits */
72 }
73 else
74 {
75 a <<= (DBL_MANT_DIG - sd);
76 /* a is now rounded to DBL_MANT_DIG bits */
77 }
78 double_bits fb;
79 fb.u.s.high = ((su_int)s & 0x80000000) | /* sign */
80 ((e + 1023) << 20) | /* exponent */
81 ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */
82 fb.u.s.low = (su_int)a; /* mantissa-low */
83 return fb.f;
84 }
85
86 #endif
87