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)
29COMPILER_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