1 /* ===-- floatuntixf.c - Implement __floatuntixf ---------------------------===
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 __floatuntixf 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 long double, rounding toward even. */
21
22 /* Assumption: long double is a IEEE 80 bit floating point type padded to 128 bits
23 * tu_int is a 128 bit integral type
24 */
25
26 /* gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee eeee |
27 * 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm
28 */
29
30 si_int __clzti2(ti_int a);
31
32 long double
__floatuntixf(tu_int a)33 __floatuntixf(tu_int a)
34 {
35 if (a == 0)
36 return 0.0;
37 const unsigned N = sizeof(tu_int) * CHAR_BIT;
38 int sd = N - __clzti2(a); /* number of significant digits */
39 int e = sd - 1; /* exponent */
40 if (sd > LDBL_MANT_DIG)
41 {
42 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
43 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
44 * 12345678901234567890123456
45 * 1 = msb 1 bit
46 * P = bit LDBL_MANT_DIG-1 bits to the right of 1
47 * Q = bit LDBL_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 LDBL_MANT_DIG + 1:
53 a <<= 1;
54 break;
55 case LDBL_MANT_DIG + 2:
56 break;
57 default:
58 a = (a >> (sd - (LDBL_MANT_DIG+2))) |
59 ((a & ((tu_int)(-1) >> ((N + LDBL_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 LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits */
66 if (a & ((tu_int)1 << LDBL_MANT_DIG))
67 {
68 a >>= 1;
69 ++e;
70 }
71 /* a is now rounded to LDBL_MANT_DIG bits */
72 }
73 else
74 {
75 a <<= (LDBL_MANT_DIG - sd);
76 /* a is now rounded to LDBL_MANT_DIG bits */
77 }
78 long_double_bits fb;
79 fb.u.high.s.low = (e + 16383); /* exponent */
80 fb.u.low.all = (du_int)a; /* mantissa */
81 return fb.f;
82 }
83
84 #endif
85