1 /* ===-- floatuntisf.c - Implement __floatuntisf ---------------------------===
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 __floatuntisf 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 float, rounding toward even. */
20
21 /* Assumption: float is a IEEE 32 bit floating point type
22 * tu_int is a 128 bit integral type
23 */
24
25 /* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */
26
27 COMPILER_RT_ABI float
__floatuntisf(tu_int a)28 __floatuntisf(tu_int a)
29 {
30 if (a == 0)
31 return 0.0F;
32 const unsigned N = sizeof(tu_int) * CHAR_BIT;
33 int sd = N - __clzti2(a); /* number of significant digits */
34 int e = sd - 1; /* exponent */
35 if (sd > FLT_MANT_DIG)
36 {
37 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
38 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
39 * 12345678901234567890123456
40 * 1 = msb 1 bit
41 * P = bit FLT_MANT_DIG-1 bits to the right of 1
42 * Q = bit FLT_MANT_DIG bits to the right of 1
43 * R = "or" of all bits to the right of Q
44 */
45 switch (sd)
46 {
47 case FLT_MANT_DIG + 1:
48 a <<= 1;
49 break;
50 case FLT_MANT_DIG + 2:
51 break;
52 default:
53 a = (a >> (sd - (FLT_MANT_DIG+2))) |
54 ((a & ((tu_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
55 };
56 /* finish: */
57 a |= (a & 4) != 0; /* Or P into R */
58 ++a; /* round - this step may add a significant bit */
59 a >>= 2; /* dump Q and R */
60 /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
61 if (a & ((tu_int)1 << FLT_MANT_DIG))
62 {
63 a >>= 1;
64 ++e;
65 }
66 /* a is now rounded to FLT_MANT_DIG bits */
67 }
68 else
69 {
70 a <<= (FLT_MANT_DIG - sd);
71 /* a is now rounded to FLT_MANT_DIG bits */
72 }
73 float_bits fb;
74 fb.u = ((e + 127) << 23) | /* exponent */
75 ((su_int)a & 0x007FFFFF); /* mantissa */
76 return fb.f;
77 }
78
79 #endif /* CRT_HAS_128BIT */
80