780530fd75
We break this down into two simplification rules: - (X + n) % n ==> X % N if X + N does not overflow. - X % n ==> X if X < n. PiperOrigin-RevId: 256907449
103 lines
3.5 KiB
C++
103 lines
3.5 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_COMPILER_XLA_OVERFLOW_UTIL_H_
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#define TENSORFLOW_COMPILER_XLA_OVERFLOW_UTIL_H_
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#include <type_traits>
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#include "absl/types/optional.h"
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#include "tensorflow/compiler/xla/xla_data.pb.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 xla {
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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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// Computes x + y and returns nullopt if it overflows.
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//
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// x and y must be signed integers.
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template <typename T>
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inline absl::optional<T> OverflowSafeAdd(T x, T y) {
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static_assert(std::is_signed<T>::value,
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"Only implemented for signed numbers T.");
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static_assert(std::is_integral<T>::value, "Only implemented for integers T.");
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// "Signed integer overflow occurs on integer addition iff the operands have
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// the same sign and the sum has a sign opposite to that of the operands."
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// Hacker's Delight 2nd ed, p 28.
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using U = typename std::make_unsigned<T>::type;
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const U ux = x;
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const U uy = y;
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const U usum = ux + uy;
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const T sum = usum;
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if (x >= 0 == y >= 0 && sum >= 0 != x >= 0) {
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return absl::nullopt;
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}
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return sum;
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}
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inline bool FitsInIntegralType(int64 x, PrimitiveType ty) {
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switch (ty) {
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case S8:
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return std::numeric_limits<int8>::min() <= x &&
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std::numeric_limits<int8>::max() >= x;
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case S16:
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return std::numeric_limits<int16>::min() <= x &&
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std::numeric_limits<int16>::max() >= x;
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case S32:
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return std::numeric_limits<int32>::min() <= x &&
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std::numeric_limits<int32>::max() >= x;
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case S64:
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return true;
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case U8:
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return 0 <= x && std::numeric_limits<uint8>::max() >= x;
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case U16:
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return 0 <= x && std::numeric_limits<uint16>::max() >= x;
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case U32:
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return 0 <= x && std::numeric_limits<uint32>::max() >= x;
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case U64:
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return 0 <= x;
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default:
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LOG(FATAL) << "Invalid primitive type " << PrimitiveType_Name(ty);
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}
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}
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} // namespace xla
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#endif // TENSORFLOW_COMPILER_XLA_OVERFLOW_UTIL_H_
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