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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;
}
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