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 //===-- lib/builtins/ppc/fixunstfti.c - Convert long double->int128 *-C -*-===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// // // This file implements converting the 128bit IBM/PowerPC long double (double- // double) data type to an unsigned 128 bit integer. // //===----------------------------------------------------------------------===// #include "../int_math.h" #define BIAS 1023 // Convert long double into an unsigned 128-bit integer. __uint128_t __fixunstfti(long double input) { // If we are trying to convert a NaN, return the NaN bit pattern. if (crt_isnan(input)) { return ((__uint128_t)0x7FF8000000000000ll) << 64 | (__uint128_t)0x0000000000000000ll; } __uint128_t result, hiResult, loResult; int hiExponent, loExponent, shift; // The long double representation, with the high and low portions of // the long double, and the corresponding bit patterns of each double. union { long double ld; double d[2]; // [0] is the high double, [1] is the low double. unsigned long long ull[2]; // High and low doubles as 64-bit integers. } ldUnion; // If the long double is less than 1.0 or negative, // return 0. if (input < 1.0) return 0; // Retrieve the 64-bit patterns of high and low doubles. // Compute the unbiased exponent of both high and low doubles by // removing the signs, isolating the exponent, and subtracting // the bias from it. ldUnion.ld = input; hiExponent = ((ldUnion.ull[0] & 0x7FFFFFFFFFFFFFFFll) >> 52) - BIAS; loExponent = ((ldUnion.ull[1] & 0x7FFFFFFFFFFFFFFFll) >> 52) - BIAS; // Convert each double into int64; they will be added to the int128 result. // CASE 1: High or low double fits in int64 // - Convert the each double normally into int64. // // CASE 2: High or low double does not fit in int64 // - Scale the double to fit within a 64-bit integer // - Calculate the shift (amount to scale the double by in the int128) // - Clear all the bits of the exponent (with 0x800FFFFFFFFFFFFF) // - Add BIAS+53 (0x4350000000000000) to exponent to correct the value // - Scale (move) the double to the correct place in the int128 // (Move it by 2^53 places) // // Note: If the high double is assumed to be positive, an unsigned conversion // from long double to 64-bit integer is needed. The low double can be either // positive or negative, so a signed conversion is needed to retain the result // of the low double and to ensure it does not simply get converted to 0. // CASE 1 - High double fits in int64. if (hiExponent < 63) { hiResult = (unsigned long long)ldUnion.d[0]; } else if (hiExponent < 128) { // CASE 2 - High double does not fit in int64, scale and convert it. shift = hiExponent - 54; ldUnion.ull[0] &= 0x800FFFFFFFFFFFFFll; ldUnion.ull[0] |= 0x4350000000000000ll; hiResult = (unsigned long long)ldUnion.d[0]; hiResult <<= shift; } else { // Detect cases for overflow. When the exponent of the high // double is greater than 128 bits and when the long double // input is positive, return the max 128-bit integer. // For negative inputs with exponents > 128, return 1, like gcc. if (ldUnion.d[0] > 0) { return ((__uint128_t)0xFFFFFFFFFFFFFFFFll) << 64 | (__uint128_t)0xFFFFFFFFFFFFFFFFll; } else { return ((__uint128_t)0x0000000000000000ll) << 64 | (__uint128_t)0x0000000000000001ll; } } // CASE 1 - Low double fits in int64. if (loExponent < 63) { loResult = (long long)ldUnion.d[1]; } else { // CASE 2 - Low double does not fit in int64, scale and convert it. shift = loExponent - 54; ldUnion.ull[1] &= 0x800FFFFFFFFFFFFFll; ldUnion.ull[1] |= 0x4350000000000000ll; loResult = (long long)ldUnion.d[1]; loResult <<= shift; } // If the low double is negative, it may change the integer value of the // whole number if the absolute value of its fractional part is bigger than // the fractional part of the high double. Because both doubles cannot // overlap, this situation only occurs when the high double has no // fractional part. ldUnion.ld = input; if ((ldUnion.d[0] == (double)hiResult) && (ldUnion.d[1] < (double)((__int128_t)loResult))) loResult--; // Add the high and low doublewords together to form a 128 bit integer. result = loResult + hiResult; return result; }