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 long double __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  long_double_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