1//===-- floattixf.c - Implement __floattixf -------------------------------===//
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 __floattixf 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 long double, rounding toward even.
18
19// Assumption: long double is a IEEE 80 bit floating point type padded to 128
20// bits ti_int is a 128 bit integral type
21
22// gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee
23// eeee | 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm
24// mmmm mmmm mmmm
25
26COMPILER_RT_ABI xf_float __floattixf(ti_int a) {
27 if (a == 0)
28 return 0.0;
29 const unsigned N = sizeof(ti_int) * CHAR_BIT;
30 const ti_int s = a >> (N - 1);
31 a = (a ^ s) - s;
32 int sd = N - __clzti2(a); // number of significant digits
33 int e = sd - 1; // exponent
34 if (sd > LDBL_MANT_DIG) {
35 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
36 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
37 // 12345678901234567890123456
38 // 1 = msb 1 bit
39 // P = bit LDBL_MANT_DIG-1 bits to the right of 1
40 // Q = bit LDBL_MANT_DIG bits to the right of 1
41 // R = "or" of all bits to the right of Q
42 switch (sd) {
43 case LDBL_MANT_DIG + 1:
44 a <<= 1;
45 break;
46 case LDBL_MANT_DIG + 2:
47 break;
48 default:
49 a = ((tu_int)a >> (sd - (LDBL_MANT_DIG + 2))) |
50 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG + 2) - sd))) != 0);
51 };
52 // finish:
53 a |= (a & 4) != 0; // Or P into R
54 ++a; // round - this step may add a significant bit
55 a >>= 2; // dump Q and R
56 // a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits
57 if (a & ((tu_int)1 << LDBL_MANT_DIG)) {
58 a >>= 1;
59 ++e;
60 }
61 // a is now rounded to LDBL_MANT_DIG bits
62 } else {
63 a <<= (LDBL_MANT_DIG - sd);
64 // a is now rounded to LDBL_MANT_DIG bits
65 }
66 xf_bits fb;
67 fb.u.high.s.low = ((su_int)s & 0x8000) | // sign
68 (e + 16383); // exponent
69 fb.u.low.all = (du_int)a; // mantissa
70 return fb.f;
71}
72
73#endif // CRT_HAS_128BIT
74

source code of compiler-rt/lib/builtins/floattixf.c