1 //===-- lib/floattitf.c - int128 -> 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 ti_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 ti_int to a fp_t, rounding toward even.
20
21 // Assumption: fp_t is a IEEE 128 bit floating point type
22 // ti_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)
__floattitf(ti_int a)29 COMPILER_RT_ABI fp_t __floattitf(ti_int a) {
30 if (a == 0)
31 return 0.0;
32 const unsigned N = sizeof(ti_int) * CHAR_BIT;
33 const ti_int s = a >> (N - 1);
34 a = (a ^ s) - s;
35 int sd = N - __clzti2(a); // number of significant digits
36 int e = sd - 1; // exponent
37 if (sd > LDBL_MANT_DIG) {
38 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
39 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
40 // 12345678901234567890123456
41 // 1 = msb 1 bit
42 // P = bit LDBL_MANT_DIG-1 bits to the right of 1
43 // Q = bit LDBL_MANT_DIG bits to the right of 1
44 // R = "or" of all bits to the right of Q
45 switch (sd) {
46 case LDBL_MANT_DIG + 1:
47 a <<= 1;
48 break;
49 case LDBL_MANT_DIG + 2:
50 break;
51 default:
52 a = ((tu_int)a >> (sd - (LDBL_MANT_DIG + 2))) |
53 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG + 2) - sd))) != 0);
54 };
55 // finish:
56 a |= (a & 4) != 0; // Or P into R
57 ++a; // round - this step may add a significant bit
58 a >>= 2; // dump Q and R
59 // a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits
60 if (a & ((tu_int)1 << LDBL_MANT_DIG)) {
61 a >>= 1;
62 ++e;
63 }
64 // a is now rounded to LDBL_MANT_DIG bits
65 } else {
66 a <<= (LDBL_MANT_DIG - sd);
67 // a is now rounded to LDBL_MANT_DIG bits
68 }
69
70 long_double_bits fb;
71 fb.u.high.all = (s & 0x8000000000000000LL) // sign
72 | (du_int)(e + 16383) << 48 // exponent
73 | ((a >> 64) & 0x0000ffffffffffffLL); // significand
74 fb.u.low.all = (du_int)(a);
75 return fb.f;
76 }
77
78 #endif
79