1//===-- lib/builtins/ppc/fixunstfti.c - Convert long double->int128 *-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 converting the 128bit IBM/PowerPC long double (double-
10// double) data type to an unsigned 128 bit integer.
11//
12//===----------------------------------------------------------------------===//
13
14#include "../int_math.h"
15#define BIAS 1023
16
17// Convert long double into an unsigned 128-bit integer.
18__uint128_t __fixunstfti(long double input) {
19
20  // If we are trying to convert a NaN, return the NaN bit pattern.
21  if (crt_isnan(input)) {
22    return ((__uint128_t)0x7FF8000000000000ll) << 64 |
23           (__uint128_t)0x0000000000000000ll;
24  }
25
26  __uint128_t result, hiResult, loResult;
27  int hiExponent, loExponent, shift;
28  // The long double representation, with the high and low portions of
29  // the long double, and the corresponding bit patterns of each double.
30  union {
31    long double ld;
32    double d[2];               // [0] is the high double, [1] is the low double.
33    unsigned long long ull[2]; // High and low doubles as 64-bit integers.
34  } ldUnion;
35
36  // If the long double is less than 1.0 or negative,
37  // return 0.
38  if (input < 1.0)
39    return 0;
40
41  // Retrieve the 64-bit patterns of high and low doubles.
42  // Compute the unbiased exponent of both high and low doubles by
43  // removing the signs, isolating the exponent, and subtracting
44  // the bias from it.
45  ldUnion.ld = input;
46  hiExponent = ((ldUnion.ull[0] & 0x7FFFFFFFFFFFFFFFll) >> 52) - BIAS;
47  loExponent = ((ldUnion.ull[1] & 0x7FFFFFFFFFFFFFFFll) >> 52) - BIAS;
48
49  // Convert each double into int64; they will be added to the int128 result.
50  // CASE 1: High or low double fits in int64
51  //      - Convert the each double normally into int64.
52  //
53  // CASE 2: High or low double does not fit in int64
54  //      - Scale the double to fit within a 64-bit integer
55  //      - Calculate the shift (amount to scale the double by in the int128)
56  //      - Clear all the bits of the exponent (with 0x800FFFFFFFFFFFFF)
57  //      - Add BIAS+53 (0x4350000000000000) to exponent to correct the value
58  //      - Scale (move) the double to the correct place in the int128
59  //        (Move it by 2^53 places)
60  //
61  // Note: If the high double is assumed to be positive, an unsigned conversion
62  // from long double to 64-bit integer is needed. The low double can be either
63  // positive or negative, so a signed conversion is needed to retain the result
64  // of the low double and to ensure it does not simply get converted to 0.
65
66  // CASE 1 - High double fits in int64.
67  if (hiExponent < 63) {
68    hiResult = (unsigned long long)ldUnion.d[0];
69  } else if (hiExponent < 128) {
70    // CASE 2 - High double does not fit in int64, scale and convert it.
71    shift = hiExponent - 54;
72    ldUnion.ull[0] &= 0x800FFFFFFFFFFFFFll;
73    ldUnion.ull[0] |= 0x4350000000000000ll;
74    hiResult = (unsigned long long)ldUnion.d[0];
75    hiResult <<= shift;
76  } else {
77    // Detect cases for overflow. When the exponent of the high
78    // double is greater than 128 bits and when the long double
79    // input is positive, return the max 128-bit integer.
80    // For negative inputs with exponents > 128, return 1, like gcc.
81    if (ldUnion.d[0] > 0) {
82      return ((__uint128_t)0xFFFFFFFFFFFFFFFFll) << 64 |
83             (__uint128_t)0xFFFFFFFFFFFFFFFFll;
84    } else {
85      return ((__uint128_t)0x0000000000000000ll) << 64 |
86             (__uint128_t)0x0000000000000001ll;
87    }
88  }
89
90  // CASE 1 - Low double fits in int64.
91  if (loExponent < 63) {
92    loResult = (long long)ldUnion.d[1];
93  } else {
94    // CASE 2 - Low double does not fit in int64, scale and convert it.
95    shift = loExponent - 54;
96    ldUnion.ull[1] &= 0x800FFFFFFFFFFFFFll;
97    ldUnion.ull[1] |= 0x4350000000000000ll;
98    loResult = (long long)ldUnion.d[1];
99    loResult <<= shift;
100  }
101
102  // If the low double is negative, it may change the integer value of the
103  // whole number if the absolute value of its fractional part is bigger than
104  // the fractional part of the high double. Because both doubles cannot
105  // overlap, this situation only occurs when the high double has no
106  // fractional part.
107  ldUnion.ld = input;
108  if ((ldUnion.d[0] == (double)hiResult) &&
109      (ldUnion.d[1] < (double)((__int128_t)loResult)))
110    loResult--;
111
112  // Add the high and low doublewords together to form a 128 bit integer.
113  result = loResult + hiResult;
114  return result;
115}
116