1 /*===-- floatdisf.c - Implement __floatdisf -------------------------------===
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 __floatdisf for the compiler_rt library.
11 *
12 *===----------------------------------------------------------------------===
13 */
14
15 /* Returns: convert a to a float, rounding toward even.*/
16
17 /* Assumption: float is a IEEE 32 bit floating point type
18 * di_int is a 64 bit integral type
19 */
20
21 /* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */
22
23 #include "int_lib.h"
24
ARM_EABI_FNALIAS(l2f,floatdisf)25 ARM_EABI_FNALIAS(l2f, floatdisf)
26
27 COMPILER_RT_ABI float
28 __floatdisf(di_int a)
29 {
30 if (a == 0)
31 return 0.0F;
32 const unsigned N = sizeof(di_int) * CHAR_BIT;
33 const di_int s = a >> (N-1);
34 a = (a ^ s) - s;
35 int sd = N - __builtin_clzll(a); /* number of significant digits */
36 int e = sd - 1; /* exponent */
37 if (sd > FLT_MANT_DIG)
38 {
39 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
40 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
41 * 12345678901234567890123456
42 * 1 = msb 1 bit
43 * P = bit FLT_MANT_DIG-1 bits to the right of 1
44 * Q = bit FLT_MANT_DIG bits to the right of 1
45 * R = "or" of all bits to the right of Q
46 */
47 switch (sd)
48 {
49 case FLT_MANT_DIG + 1:
50 a <<= 1;
51 break;
52 case FLT_MANT_DIG + 2:
53 break;
54 default:
55 a = ((du_int)a >> (sd - (FLT_MANT_DIG+2))) |
56 ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
57 };
58 /* finish: */
59 a |= (a & 4) != 0; /* Or P into R */
60 ++a; /* round - this step may add a significant bit */
61 a >>= 2; /* dump Q and R */
62 /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
63 if (a & ((du_int)1 << FLT_MANT_DIG))
64 {
65 a >>= 1;
66 ++e;
67 }
68 /* a is now rounded to FLT_MANT_DIG bits */
69 }
70 else
71 {
72 a <<= (FLT_MANT_DIG - sd);
73 /* a is now rounded to FLT_MANT_DIG bits */
74 }
75 float_bits fb;
76 fb.u = ((su_int)s & 0x80000000) | /* sign */
77 ((e + 127) << 23) | /* exponent */
78 ((su_int)a & 0x007FFFFF); /* mantissa */
79 return fb.f;
80 }
81