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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "builtin/temporal/Int96.h"
#include "mozilla/Assertions.h"
#include "mozilla/Casting.h"
#include "mozilla/FloatingPoint.h"
#include "mozilla/Maybe.h"
#include <cmath>
#include <stddef.h>
#include <stdint.h>
#include "jsnum.h"
using namespace js;
using namespace js::temporal;
mozilla::Maybe<Int96> Int96::fromInteger(double value) {
MOZ_ASSERT(IsInteger(value));
// Fast path for the common case.
int64_t intValue;
if (mozilla::NumberEqualsInt64(value, &intValue)) {
return mozilla::Some(Int96{intValue});
}
// First double integer which requires more than three digits.
constexpr double maximum = 0x1p+96;
// Reject if the value needs more than 96 bits.
if (std::abs(value) >= maximum) {
return mozilla::Nothing();
}
// Inlined version of |BigInt::createFromDouble()| for DigitBits=32. See the
// comments in |BigInt::createFromDouble()| for how this code works.
constexpr size_t DigitBits = 32;
// The number can't have more than three digits when it's below |maximum|.
Int96::Digits digits = {};
int exponent = mozilla::ExponentComponent(value);
MOZ_ASSERT(0 <= exponent && exponent <= 95,
"exponent is lower than exponent of 0x1p+96");
int length = exponent / DigitBits + 1;
MOZ_ASSERT(1 <= length && length <= 3);
using Double = mozilla::FloatingPoint<double>;
uint64_t mantissa =
mozilla::BitwiseCast<uint64_t>(value) & Double::kSignificandBits;
// Add implicit high bit.
mantissa |= 1ull << Double::kSignificandWidth;
// 0-indexed position of the double's most significant bit within the `msd`.
int msdTopBit = exponent % DigitBits;
// First, build the MSD by shifting the mantissa appropriately.
int remainingMantissaBits = Double::kSignificandWidth - msdTopBit;
digits[--length] = mantissa >> remainingMantissaBits;
// Fill in digits containing mantissa contributions.
mantissa = mantissa << (64 - remainingMantissaBits);
if (mantissa) {
MOZ_ASSERT(length > 0);
digits[--length] = uint32_t(mantissa >> 32);
if (uint32_t(mantissa)) {
MOZ_ASSERT(length > 0);
digits[--length] = uint32_t(mantissa);
}
}
return mozilla::Some(Int96{digits, value < 0});
}
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