1//===-- int_to_fp_impl.inc - integer to floating point conversion ---------===//
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// Thsi file implements a generic conversion from an integer type to an
10// IEEE-754 floating point type, allowing a common implementation to be hsared
11// without copy and paste.
12//
13//===----------------------------------------------------------------------===//
14
15#include "int_to_fp.h"
16
17static __inline dst_t __floatXiYf__(src_t a) {
18  if (a == 0)
19    return 0.0;
20
21  enum {
22    dstMantDig = dstSigBits + 1,
23    srcBits = sizeof(src_t) * CHAR_BIT,
24    srcIsSigned = ((src_t)-1) < 0,
25  };
26
27  const src_t s = srcIsSigned ? a >> (srcBits - 1) : 0;
28
29  a = (usrc_t)(a ^ s) - s;
30  int sd = srcBits - clzSrcT(a);         // number of significant digits
31  int e = sd - 1;                        // exponent
32  if (sd > dstMantDig) {
33    //  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
34    //  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
35    //                                                12345678901234567890123456
36    //  1 = msb 1 bit
37    //  P = bit dstMantDig-1 bits to the right of 1
38    //  Q = bit dstMantDig bits to the right of 1
39    //  R = "or" of all bits to the right of Q
40    if (sd == dstMantDig + 1) {
41      a <<= 1;
42    } else if (sd == dstMantDig + 2) {
43      // Do nothing.
44    } else {
45      a = ((usrc_t)a >> (sd - (dstMantDig + 2))) |
46          ((a & ((usrc_t)(-1) >> ((srcBits + dstMantDig + 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 dstMantDig or dstMantDig+1 bits
53    if (a & ((usrc_t)1 << dstMantDig)) {
54      a >>= 1;
55      ++e;
56    }
57    // a is now rounded to dstMantDig bits
58  } else {
59    a <<= (dstMantDig - sd);
60    // a is now rounded to dstMantDig bits
61  }
62  const int dstBits = sizeof(dst_t) * CHAR_BIT;
63  const dst_rep_t dstSignMask = DST_REP_C(1) << (dstBits - 1);
64  const int dstExpBits = dstBits - dstSigBits - 1;
65  const int dstExpBias = (1 << (dstExpBits - 1)) - 1;
66  const dst_rep_t dstSignificandMask = (DST_REP_C(1) << dstSigBits) - 1;
67  // Combine sign, exponent, and mantissa.
68  const dst_rep_t result = ((dst_rep_t)s & dstSignMask) |
69                           ((dst_rep_t)(e + dstExpBias) << dstSigBits) |
70                           ((dst_rep_t)(a) & dstSignificandMask);
71  return dstFromRep(result);
72}
73