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/*
* Copyright 2018 Google
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "Firestore/core/src/firebase/firestore/util/comparison.h"
#include <cmath>
#include <limits>
using std::isnan;
namespace firebase {
namespace firestore {
namespace util {
bool Comparator<absl::string_view>::operator()(
const absl::string_view& left, const absl::string_view& right) const {
// TODO(wilhuff): truncation aware comparison
return left < right;
}
bool Comparator<std::string>::operator()(const std::string& left,
const std::string& right) const {
// TODO(wilhuff): truncation aware comparison
return left < right;
}
bool Comparator<double>::operator()(double left, double right) const {
// NaN sorts equal to itself and before any other number.
if (left < right) {
return true;
} else if (left >= right) {
return false;
} else {
// One or both left and right is NaN.
return isnan(left) && !isnan(right);
}
}
static constexpr double INT64_MIN_VALUE_AS_DOUBLE =
static_cast<double>(std::numeric_limits<int64_t>::min());
static constexpr double INT64_MAX_VALUE_AS_DOUBLE =
static_cast<double>(std::numeric_limits<int64_t>::max());
ComparisonResult CompareMixedNumber(double double_value, int64_t int64_value) {
// LLONG_MIN has an exact representation as double, so to check for a value
// outside the range representable by long, we have to check for strictly less
// than LLONG_MIN. Note that this also handles negative infinity.
if (double_value < INT64_MIN_VALUE_AS_DOUBLE) {
return ComparisonResult::Ascending;
}
// LLONG_MAX has no exact representation as double (casting as we've done
// makes 2^63, which is larger than LLONG_MAX), so consider any value greater
// than or equal to the threshold to be out of range. This also handles
// positive infinity.
if (double_value >= INT64_MAX_VALUE_AS_DOUBLE) {
return ComparisonResult::Descending;
}
// In Firestore NaN is defined to compare before all other numbers.
if (isnan(double_value)) {
return ComparisonResult::Ascending;
}
auto double_as_int64 = static_cast<int64_t>(double_value);
ComparisonResult cmp = Compare<int64_t>(double_as_int64, int64_value);
if (cmp != ComparisonResult::Same) {
return cmp;
}
// At this point the long representations are equal but this could be due to
// rounding.
auto int64_as_double = static_cast<double>(int64_value);
return Compare<double>(double_value, int64_as_double);
}
/** Helper to normalize a double and then return the raw bits as a uint64_t. */
uint64_t DoubleBits(double d) {
if (isnan(d)) {
d = NAN;
}
// Unlike C, C++ does not define type punning through a union type.
// TODO(wilhuff): replace with absl::bit_cast
static_assert(sizeof(double) == sizeof(uint64_t), "doubles must be 8 bytes");
uint64_t bits;
memcpy(&bits, &d, sizeof(bits));
return bits;
}
bool DoubleBitwiseEquals(double left, double right) {
return DoubleBits(left) == DoubleBits(right);
}
size_t DoubleBitwiseHash(double d) {
uint64_t bits = DoubleBits(d);
// Note that x ^ (x >> 32) works fine for both 32 and 64 bit definitions of
// size_t
return static_cast<size_t>(bits) ^ static_cast<size_t>(bits >> 32);
}
} // namespace util
} // namespace firestore
} // namespace firebase
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