192 lines
9.0 KiB
C++
192 lines
9.0 KiB
C++
// This file is part of Eigen, a lightweight C++ template library
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// for linear algebra.
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//
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// Copyright (C) 2020 C. Antonio Sanchez <cantonios@google.com>
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//
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// This Source Code Form is subject to the terms of the Mozilla
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// Public License v. 2.0. If a copy of the MPL was not distributed
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// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
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// Utilities for generating random numbers without overflows, which might
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// otherwise result in undefined behavior.
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namespace Eigen {
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namespace internal {
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// Default implementation assuming SrcScalar fits into TgtScalar.
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template <typename SrcScalar, typename TgtScalar, typename EnableIf = void>
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struct random_without_cast_overflow {
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static SrcScalar value() { return internal::random<SrcScalar>(); }
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};
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// Signed to unsigned integer widening cast.
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar,
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std::enable_if_t<NumTraits<SrcScalar>::IsInteger && NumTraits<SrcScalar>::IsSigned &&
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NumTraits<TgtScalar>::IsInteger && !NumTraits<TgtScalar>::IsSigned &&
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(std::numeric_limits<SrcScalar>::digits < std::numeric_limits<TgtScalar>::digits ||
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(std::numeric_limits<SrcScalar>::digits == std::numeric_limits<TgtScalar>::digits &&
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NumTraits<SrcScalar>::IsSigned))>> {
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static SrcScalar value() {
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SrcScalar a = internal::random<SrcScalar>();
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return a < SrcScalar(0) ? -(a + 1) : a;
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}
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};
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// Signed to unsigned integer widening cast.
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar,
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std::enable_if_t<NumTraits<SrcScalar>::IsInteger && !NumTraits<SrcScalar>::IsSigned &&
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NumTraits<TgtScalar>::IsInteger && !NumTraits<TgtScalar>::IsSigned &&
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(std::numeric_limits<SrcScalar>::digits < std::numeric_limits<TgtScalar>::digits ||
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(std::numeric_limits<SrcScalar>::digits == std::numeric_limits<TgtScalar>::digits &&
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NumTraits<SrcScalar>::IsSigned))>> {
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static SrcScalar value() {
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SrcScalar a = internal::random<SrcScalar>();
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return a;
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}
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};
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// Integer to unsigned narrowing cast.
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar,
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std::enable_if_t<NumTraits<SrcScalar>::IsInteger && NumTraits<TgtScalar>::IsInteger &&
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NumTraits<TgtScalar>::IsSigned && !NumTraits<SrcScalar>::IsSigned &&
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(std::numeric_limits<SrcScalar>::digits > std::numeric_limits<TgtScalar>::digits)>> {
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static SrcScalar value() {
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TgtScalar b = internal::random<TgtScalar>();
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return static_cast<SrcScalar>(b < TgtScalar(0) ? -(b + 1) : b);
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}
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};
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// Integer to unsigned narrowing cast.
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar,
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std::enable_if_t<NumTraits<SrcScalar>::IsInteger && NumTraits<TgtScalar>::IsInteger &&
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!NumTraits<TgtScalar>::IsSigned && !NumTraits<SrcScalar>::IsSigned &&
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(std::numeric_limits<SrcScalar>::digits > std::numeric_limits<TgtScalar>::digits)>> {
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static SrcScalar value() {
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TgtScalar b = internal::random<TgtScalar>();
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return static_cast<SrcScalar>(b);
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}
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};
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// Integer to signed narrowing cast.
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar,
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std::enable_if_t<NumTraits<SrcScalar>::IsInteger && NumTraits<TgtScalar>::IsInteger &&
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NumTraits<SrcScalar>::IsSigned &&
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(std::numeric_limits<SrcScalar>::digits > std::numeric_limits<TgtScalar>::digits)>> {
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static SrcScalar value() { return static_cast<SrcScalar>(internal::random<TgtScalar>()); }
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};
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// Unsigned to signed integer narrowing cast.
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar,
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std::enable_if_t<NumTraits<SrcScalar>::IsInteger && NumTraits<TgtScalar>::IsInteger &&
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!NumTraits<SrcScalar>::IsSigned && NumTraits<TgtScalar>::IsSigned &&
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(std::numeric_limits<SrcScalar>::digits == std::numeric_limits<TgtScalar>::digits)>> {
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static SrcScalar value() { return internal::random<SrcScalar>() / 2; }
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};
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// Floating-point to integer, full precision.
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar,
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std::enable_if_t<!NumTraits<SrcScalar>::IsInteger && !NumTraits<SrcScalar>::IsComplex &&
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NumTraits<TgtScalar>::IsInteger &&
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(std::numeric_limits<TgtScalar>::digits <= std::numeric_limits<SrcScalar>::digits)>> {
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static SrcScalar value() { return static_cast<SrcScalar>(internal::random<TgtScalar>()); }
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};
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// Floating-point to integer, narrowing precision.
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar,
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std::enable_if_t<!NumTraits<SrcScalar>::IsInteger && !NumTraits<SrcScalar>::IsComplex &&
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NumTraits<TgtScalar>::IsInteger && NumTraits<TgtScalar>::IsSigned &&
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(std::numeric_limits<TgtScalar>::digits > std::numeric_limits<SrcScalar>::digits)>> {
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static SrcScalar value() {
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// NOTE: internal::random<T>() is limited by RAND_MAX, so random<int64_t> is always within that range.
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// This prevents us from simply shifting bits, which would result in only 0 or -1.
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// Instead, keep least-significant K bits and sign.
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static const TgtScalar KeepMask = (static_cast<TgtScalar>(1) << std::numeric_limits<SrcScalar>::digits) - 1;
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const TgtScalar a = internal::random<TgtScalar>();
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return static_cast<SrcScalar>(a > TgtScalar(0) ? (a & KeepMask) : -(a & KeepMask));
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}
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};
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar,
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std::enable_if_t<!NumTraits<SrcScalar>::IsInteger && !NumTraits<SrcScalar>::IsComplex &&
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NumTraits<TgtScalar>::IsInteger && !NumTraits<TgtScalar>::IsSigned &&
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(std::numeric_limits<TgtScalar>::digits > std::numeric_limits<SrcScalar>::digits)>> {
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static SrcScalar value() {
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// NOTE: internal::random<T>() is limited by RAND_MAX, so random<int64_t> is always within that range.
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// This prevents us from simply shifting bits, which would result in only 0 or -1.
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// Instead, keep least-significant K bits and sign.
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static const TgtScalar KeepMask = (static_cast<TgtScalar>(1) << std::numeric_limits<SrcScalar>::digits) - 1;
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const TgtScalar a = internal::random<TgtScalar>();
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return static_cast<SrcScalar>(a & KeepMask);
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}
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};
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// Integer to floating-point, re-use above logic.
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar,
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std::enable_if_t<NumTraits<SrcScalar>::IsInteger && !NumTraits<TgtScalar>::IsInteger &&
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!NumTraits<TgtScalar>::IsComplex>> {
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static SrcScalar value() {
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return static_cast<SrcScalar>(random_without_cast_overflow<TgtScalar, SrcScalar>::value());
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}
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};
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// Floating-point narrowing conversion.
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar,
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std::enable_if_t<!NumTraits<SrcScalar>::IsInteger && !NumTraits<SrcScalar>::IsComplex &&
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!NumTraits<TgtScalar>::IsInteger && !NumTraits<TgtScalar>::IsComplex &&
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(std::numeric_limits<SrcScalar>::digits > std::numeric_limits<TgtScalar>::digits)>> {
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static SrcScalar value() { return static_cast<SrcScalar>(internal::random<TgtScalar>()); }
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};
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// Complex to non-complex.
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar, std::enable_if_t<NumTraits<SrcScalar>::IsComplex && !NumTraits<TgtScalar>::IsComplex>> {
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typedef typename NumTraits<SrcScalar>::Real SrcReal;
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static SrcScalar value() { return SrcScalar(random_without_cast_overflow<SrcReal, TgtScalar>::value(), 0); }
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};
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// Non-complex to complex.
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar, std::enable_if_t<!NumTraits<SrcScalar>::IsComplex && NumTraits<TgtScalar>::IsComplex>> {
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typedef typename NumTraits<TgtScalar>::Real TgtReal;
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static SrcScalar value() { return random_without_cast_overflow<SrcScalar, TgtReal>::value(); }
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};
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// Complex to complex.
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template <typename SrcScalar, typename TgtScalar>
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struct random_without_cast_overflow<
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SrcScalar, TgtScalar, std::enable_if_t<NumTraits<SrcScalar>::IsComplex && NumTraits<TgtScalar>::IsComplex>> {
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typedef typename NumTraits<SrcScalar>::Real SrcReal;
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typedef typename NumTraits<TgtScalar>::Real TgtReal;
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static SrcScalar value() {
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return SrcScalar(random_without_cast_overflow<SrcReal, TgtReal>::value(),
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random_without_cast_overflow<SrcReal, TgtReal>::value());
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}
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};
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} // namespace internal
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} // namespace Eigen
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