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Edward O'Callaghan3bc7c132009-08-07 20:30:09 +00001/* ===-- floattisf.c - Implement __floattisf -------------------------------===
2 *
3 * The LLVM Compiler Infrastructure
4 *
Howard Hinnantfbe8a612010-11-16 22:13:33 +00005 * This file is dual licensed under the MIT and the University of Illinois Open
6 * Source Licenses. See LICENSE.TXT for details.
Edward O'Callaghan3bc7c132009-08-07 20:30:09 +00007 *
8 * ===----------------------------------------------------------------------===
9 *
10 * This file implements __floattisf for the compiler_rt library.
11 *
12 * ===----------------------------------------------------------------------===
13 */
Daniel Dunbard42efbe2009-06-26 16:47:03 +000014
Daniel Dunbard42efbe2009-06-26 16:47:03 +000015#include "int_lib.h"
Daniel Dunbard42efbe2009-06-26 16:47:03 +000016
Joerg Sonnenberger0cb7cbc2014-02-21 23:53:03 +000017#ifdef CRT_HAS_128BIT
Chandler Carruth18db3342012-06-22 21:09:22 +000018
Edward O'Callaghan3bc7c132009-08-07 20:30:09 +000019/* Returns: convert a to a float, rounding toward even. */
Daniel Dunbard42efbe2009-06-26 16:47:03 +000020
Edward O'Callaghan3bc7c132009-08-07 20:30:09 +000021/* Assumption: float is a IEEE 32 bit floating point type
22 * ti_int is a 128 bit integral type
23 */
Daniel Dunbard42efbe2009-06-26 16:47:03 +000024
Edward O'Callaghan3bc7c132009-08-07 20:30:09 +000025/* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */
Daniel Dunbard42efbe2009-06-26 16:47:03 +000026
Joerg Sonnenberger165d6332014-03-01 15:30:50 +000027COMPILER_RT_ABI float
Daniel Dunbard42efbe2009-06-26 16:47:03 +000028__floattisf(ti_int a)
29{
30 if (a == 0)
31 return 0.0F;
32 const unsigned N = sizeof(ti_int) * CHAR_BIT;
33 const ti_int s = a >> (N-1);
34 a = (a ^ s) - s;
Edward O'Callaghan3bc7c132009-08-07 20:30:09 +000035 int sd = N - __clzti2(a); /* number of significant digits */
36 int e = sd - 1; /* exponent */
Daniel Dunbard42efbe2009-06-26 16:47:03 +000037 if (sd > FLT_MANT_DIG)
38 {
Edward O'Callaghan3bc7c132009-08-07 20:30:09 +000039 /* 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 */
Daniel Dunbard42efbe2009-06-26 16:47:03 +000047 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 = ((tu_int)a >> (sd - (FLT_MANT_DIG+2))) |
56 ((a & ((tu_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
57 };
Edward O'Callaghan3bc7c132009-08-07 20:30:09 +000058 /* 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 */
Daniel Dunbard42efbe2009-06-26 16:47:03 +000063 if (a & ((tu_int)1 << FLT_MANT_DIG))
64 {
65 a >>= 1;
66 ++e;
67 }
Edward O'Callaghan3bc7c132009-08-07 20:30:09 +000068 /* a is now rounded to FLT_MANT_DIG bits */
Daniel Dunbard42efbe2009-06-26 16:47:03 +000069 }
70 else
71 {
72 a <<= (FLT_MANT_DIG - sd);
Edward O'Callaghan3bc7c132009-08-07 20:30:09 +000073 /* a is now rounded to FLT_MANT_DIG bits */
Daniel Dunbard42efbe2009-06-26 16:47:03 +000074 }
75 float_bits fb;
Edward O'Callaghan3bc7c132009-08-07 20:30:09 +000076 fb.u = ((su_int)s & 0x80000000) | /* sign */
77 ((e + 127) << 23) | /* exponent */
78 ((su_int)a & 0x007FFFFF); /* mantissa */
Daniel Dunbard42efbe2009-06-26 16:47:03 +000079 return fb.f;
80}
81
Joerg Sonnenberger0cb7cbc2014-02-21 23:53:03 +000082#endif /* CRT_HAS_128BIT */