1 /* ===-- floattixf.c - Implement __floattixf -------------------------------===
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 __floattixf 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 * ti_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
__floattixf(ti_int a)33 __floattixf(ti_int a)
34 {
35 if (a == 0)
36 return 0.0;
37 const unsigned N = sizeof(ti_int) * CHAR_BIT;
38 const ti_int s = a >> (N-1);
39 a = (a ^ s) - s;
40 int sd = N - __clzti2(a); /* number of significant digits */
41 int e = sd - 1; /* exponent */
42 if (sd > LDBL_MANT_DIG)
43 {
44 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
45 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
46 * 12345678901234567890123456
47 * 1 = msb 1 bit
48 * P = bit LDBL_MANT_DIG-1 bits to the right of 1
49 * Q = bit LDBL_MANT_DIG bits to the right of 1
50 * R = "or" of all bits to the right of Q
51 */
52 switch (sd)
53 {
54 case LDBL_MANT_DIG + 1:
55 a <<= 1;
56 break;
57 case LDBL_MANT_DIG + 2:
58 break;
59 default:
60 a = ((tu_int)a >> (sd - (LDBL_MANT_DIG+2))) |
61 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG+2) - sd))) != 0);
62 };
63 /* finish: */
64 a |= (a & 4) != 0; /* Or P into R */
65 ++a; /* round - this step may add a significant bit */
66 a >>= 2; /* dump Q and R */
67 /* a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits */
68 if (a & ((tu_int)1 << LDBL_MANT_DIG))
69 {
70 a >>= 1;
71 ++e;
72 }
73 /* a is now rounded to LDBL_MANT_DIG bits */
74 }
75 else
76 {
77 a <<= (LDBL_MANT_DIG - sd);
78 /* a is now rounded to LDBL_MANT_DIG bits */
79 }
80 long_double_bits fb;
81 fb.u.high.s.low = ((su_int)s & 0x8000) | /* sign */
82 (e + 16383); /* exponent */
83 fb.u.low.all = (du_int)a; /* mantissa */
84 return fb.f;
85 }
86
87 #endif
88