1 //===-- floattisf.c - Implement __floattisf -------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements __floattisf for the compiler_rt library.
10 //
11 //===----------------------------------------------------------------------===//
12
13 #include "int_lib.h"
14
15 #ifdef CRT_HAS_128BIT
16
17 // Returns: convert a to a float, rounding toward even.
18
19 // Assumption: float is a IEEE 32 bit floating point type
20 // ti_int is a 128 bit integral type
21
22 // seee eeee emmm mmmm mmmm mmmm mmmm mmmm
23
__floattisf(ti_int a)24 COMPILER_RT_ABI float __floattisf(ti_int a) {
25 if (a == 0)
26 return 0.0F;
27 const unsigned N = sizeof(ti_int) * CHAR_BIT;
28 const ti_int s = a >> (N - 1);
29 a = (a ^ s) - s;
30 int sd = N - __clzti2(a); // number of significant digits
31 int e = sd - 1; // exponent
32 if (sd > FLT_MANT_DIG) {
33 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
34 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
35 // 12345678901234567890123456
36 // 1 = msb 1 bit
37 // P = bit FLT_MANT_DIG-1 bits to the right of 1
38 // Q = bit FLT_MANT_DIG bits to the right of 1
39 // R = "or" of all bits to the right of Q
40 switch (sd) {
41 case FLT_MANT_DIG + 1:
42 a <<= 1;
43 break;
44 case FLT_MANT_DIG + 2:
45 break;
46 default:
47 a = ((tu_int)a >> (sd - (FLT_MANT_DIG + 2))) |
48 ((a & ((tu_int)(-1) >> ((N + FLT_MANT_DIG + 2) - sd))) != 0);
49 };
50 // finish:
51 a |= (a & 4) != 0; // Or P into R
52 ++a; // round - this step may add a significant bit
53 a >>= 2; // dump Q and R
54 // a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits
55 if (a & ((tu_int)1 << FLT_MANT_DIG)) {
56 a >>= 1;
57 ++e;
58 }
59 // a is now rounded to FLT_MANT_DIG bits
60 } else {
61 a <<= (FLT_MANT_DIG - sd);
62 // a is now rounded to FLT_MANT_DIG bits
63 }
64 float_bits fb;
65 fb.u = ((su_int)s & 0x80000000) | // sign
66 ((e + 127) << 23) | // exponent
67 ((su_int)a & 0x007FFFFF); // mantissa
68 return fb.f;
69 }
70
71 #endif // CRT_HAS_128BIT
72