1//===-- floatuntisf.c - Implement __floatuntisf ---------------------------===//
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 __floatuntisf 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 float, rounding toward even.
18
19// Assumption: float is a IEEE 32 bit floating point type
20//             tu_int is a 128 bit integral type
21
22// seee eeee emmm mmmm mmmm mmmm mmmm mmmm
23
24COMPILER_RT_ABI float __floatuntisf(tu_int a) {
25  if (a == 0)
26    return 0.0F;
27  const unsigned N = sizeof(tu_int) * CHAR_BIT;
28  int sd = N - __clzti2(a); // number of significant digits
29  int e = sd - 1;           // exponent
30  if (sd > FLT_MANT_DIG) {
31    //  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
32    //  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
33    //                                                12345678901234567890123456
34    //  1 = msb 1 bit
35    //  P = bit FLT_MANT_DIG-1 bits to the right of 1
36    //  Q = bit FLT_MANT_DIG bits to the right of 1
37    //  R = "or" of all bits to the right of Q
38    switch (sd) {
39    case FLT_MANT_DIG + 1:
40      a <<= 1;
41      break;
42    case FLT_MANT_DIG + 2:
43      break;
44    default:
45      a = (a >> (sd - (FLT_MANT_DIG + 2))) |
46          ((a & ((tu_int)(-1) >> ((N + FLT_MANT_DIG + 2) - sd))) != 0);
47    };
48    // finish:
49    a |= (a & 4) != 0; // Or P into R
50    ++a;               // round - this step may add a significant bit
51    a >>= 2;           // dump Q and R
52    // a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits
53    if (a & ((tu_int)1 << FLT_MANT_DIG)) {
54      a >>= 1;
55      ++e;
56    }
57    // a is now rounded to FLT_MANT_DIG bits
58  } else {
59    a <<= (FLT_MANT_DIG - sd);
60    // a is now rounded to FLT_MANT_DIG bits
61  }
62  float_bits fb;
63  fb.u = ((e + 127) << 23) |       // exponent
64         ((su_int)a & 0x007FFFFF); // mantissa
65  return fb.f;
66}
67
68#endif // CRT_HAS_128BIT
69