51 lines
1.9 KiB
C++
51 lines
1.9 KiB
C++
/* Copyright 2015 The TensorFlow Authors. All Rights Reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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==============================================================================*/
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#ifndef TENSORFLOW_CORE_UTIL_OVERFLOW_H_
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#define TENSORFLOW_CORE_UTIL_OVERFLOW_H_
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#include "tensorflow/core/platform/logging.h"
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#include "tensorflow/core/platform/macros.h"
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#include "tensorflow/core/platform/types.h"
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namespace tensorflow {
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// Multiply two nonnegative int64's, returning negative for overflow
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inline int64 MultiplyWithoutOverflow(const int64 x, const int64 y) {
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// Multiply in uint64 rather than int64 since signed overflow is undefined.
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// Negative values will wrap around to large unsigned values in the casts
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// (see section 4.7 [conv.integral] of the C++14 standard).
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const uint64 ux = x;
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const uint64 uy = y;
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const uint64 uxy = ux * uy;
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// Check if we overflow uint64, using a cheap check if both inputs are small
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if (TF_PREDICT_FALSE((ux | uy) >> 32 != 0)) {
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// Ensure nonnegativity. Note that negative numbers will appear "large"
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// to the unsigned comparisons above.
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CHECK(x >= 0 && y >= 0);
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// Otherwise, detect overflow using a division
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if (ux != 0 && uxy / ux != uy) return -1;
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}
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// Cast back to signed. Any negative value will signal an error.
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return static_cast<int64>(uxy);
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}
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} // namespace tensorflow
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#endif // TENSORFLOW_CORE_UTIL_OVERFLOW_H_
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