1//===-- floatdisf.c - Implement __floatdisf -------------------------------===//
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 __floatdisf for the compiler_rt library.
10//
11//===----------------------------------------------------------------------===//
12
13// Returns: convert a to a float, rounding toward even.
14
15// Assumption: float is a IEEE 32 bit floating point type
16//             di_int is a 64 bit integral type
17
18// seee eeee emmm mmmm mmmm mmmm mmmm mmmm
19
20#include "int_lib.h"
21
22COMPILER_RT_ABI float __floatdisf(di_int a) {
23  if (a == 0)
24    return 0.0F;
25  const unsigned N = sizeof(di_int) * CHAR_BIT;
26  const di_int s = a >> (N - 1);
27  a = (a ^ s) - s;
28  int sd = N - __builtin_clzll(a); // number of significant digits
29  si_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 = ((du_int)a >> (sd - (FLT_MANT_DIG + 2))) |
46          ((a & ((du_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 & ((du_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 = ((su_int)s & 0x80000000) | // sign
64         ((e + 127) << 23) |        // exponent
65         ((su_int)a & 0x007FFFFF);  // mantissa
66  return fb.f;
67}
68
69#if defined(__ARM_EABI__)
70#if defined(COMPILER_RT_ARMHF_TARGET)
71AEABI_RTABI float __aeabi_l2f(di_int a) { return __floatdisf(a); }
72#else
73COMPILER_RT_ALIAS(__floatdisf, __aeabi_l2f)
74#endif
75#endif
76
77#if defined(__MINGW32__) && defined(__arm__)
78COMPILER_RT_ALIAS(__floatdisf, __i64tos)
79#endif
80