1 //===-- lib/floatuntitf.c - uint128 -> quad-precision conversion --*- C -*-===//
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 tu_int to quad-precision conversion for the
10 // compiler-rt library in the IEEE-754 default round-to-nearest, ties-to-even
11 // mode.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #define QUAD_PRECISION
16 #include "fp_lib.h"
17 #include "int_lib.h"
18
19 // Returns: convert a tu_int to a fp_t, rounding toward even.
20
21 // Assumption: fp_t is a IEEE 128 bit floating point type
22 // tu_int is a 128 bit integral type
23
24 // seee eeee eeee eeee mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm
25 // mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm
26 // mmmm mmmm mmmm
27
28 #if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
__floatuntitf(tu_int a)29 COMPILER_RT_ABI fp_t __floatuntitf(tu_int a) {
30 if (a == 0)
31 return 0.0;
32 const unsigned N = sizeof(tu_int) * CHAR_BIT;
33 int sd = N - __clzti2(a); // number of significant digits
34 int e = sd - 1; // exponent
35 if (sd > LDBL_MANT_DIG) {
36 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
37 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
38 // 12345678901234567890123456
39 // 1 = msb 1 bit
40 // P = bit LDBL_MANT_DIG-1 bits to the right of 1
41 // Q = bit LDBL_MANT_DIG bits to the right of 1
42 // R = "or" of all bits to the right of Q
43 switch (sd) {
44 case LDBL_MANT_DIG + 1:
45 a <<= 1;
46 break;
47 case LDBL_MANT_DIG + 2:
48 break;
49 default:
50 a = (a >> (sd - (LDBL_MANT_DIG + 2))) |
51 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG + 2) - sd))) != 0);
52 };
53 // finish:
54 a |= (a & 4) != 0; // Or P into R
55 ++a; // round - this step may add a significant bit
56 a >>= 2; // dump Q and R
57 // a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits
58 if (a & ((tu_int)1 << LDBL_MANT_DIG)) {
59 a >>= 1;
60 ++e;
61 }
62 // a is now rounded to LDBL_MANT_DIG bits
63 } else {
64 a <<= (LDBL_MANT_DIG - sd);
65 // a is now rounded to LDBL_MANT_DIG bits
66 }
67
68 long_double_bits fb;
69 fb.u.high.all = (du_int)(e + 16383) << 48 // exponent
70 | ((a >> 64) & 0x0000ffffffffffffLL); // significand
71 fb.u.low.all = (du_int)(a);
72 return fb.f;
73 }
74
75 #endif
76