1//===-- floatuntixf.c - Implement __floatuntixf ---------------------------===//
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 __floatuntixf 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 tu_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 __floatuntixf(tu_int a) {
27 if (a == 0)
28 return 0.0;
29 const unsigned N = sizeof(tu_int) * CHAR_BIT;
30 int sd = N - __clzti2(a); // number of significant digits
31 int e = sd - 1; // exponent
32 if (sd > LDBL_MANT_DIG) {
33 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
34 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
35 // 12345678901234567890123456
36 // 1 = msb 1 bit
37 // P = bit LDBL_MANT_DIG-1 bits to the right of 1
38 // Q = bit LDBL_MANT_DIG bits to the right of 1
39 // R = "or" of all bits to the right of Q
40 switch (sd) {
41 case LDBL_MANT_DIG + 1:
42 a <<= 1;
43 break;
44 case LDBL_MANT_DIG + 2:
45 break;
46 default:
47 a = (a >> (sd - (LDBL_MANT_DIG + 2))) |
48 ((a & ((tu_int)(-1) >> ((N + LDBL_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 LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits
55 if (a & ((tu_int)1 << LDBL_MANT_DIG)) {
56 a >>= 1;
57 ++e;
58 }
59 // a is now rounded to LDBL_MANT_DIG bits
60 } else {
61 a <<= (LDBL_MANT_DIG - sd);
62 // a is now rounded to LDBL_MANT_DIG bits
63 }
64 xf_bits fb;
65 fb.u.high.s.low = (e + 16383); // exponent
66 fb.u.low.all = (du_int)a; // mantissa
67 return fb.f;
68}
69
70#endif
71

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