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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-exception6//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 102316 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 of29 // 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 by43 // removing the signs, isolating the exponent, and subtracting44 // 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 int6451 // - Convert the each double normally into int64.52 //53 // CASE 2: High or low double does not fit in int6454 // - Scale the double to fit within a 64-bit integer55 // - 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 value58 // - Scale (move) the double to the correct place in the int12859 // (Move it by 2^53 places)60 //61 // Note: If the high double is assumed to be positive, an unsigned conversion62 // from long double to 64-bit integer is needed. The low double can be either63 // positive or negative, so a signed conversion is needed to retain the result64 // 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 high78 // double is greater than 128 bits and when the long double79 // 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 the103 // whole number if the absolute value of its fractional part is bigger than104 // the fractional part of the high double. Because both doubles cannot105 // overlap, this situation only occurs when the high double has no106 // 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