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)
29COMPILER_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