wehub-resource-sync
82 lines
2.8 KiB
C++
82 lines
2.8 KiB
C++
/*
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* SPDX-FileCopyrightText: Copyright (c) 1993-2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
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* SPDX-License-Identifier: Apache-2.0
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*
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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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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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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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#include <cstdint>
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namespace nvinfer1::plugin::detail
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{
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// Count leading zeros - start from most significant bit.
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int32_t clz(int32_t x)
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{
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for (int32_t i = 31; i >= 0; --i)
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{
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if ((1U << i) & x)
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{
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return 31 - i;
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}
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}
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return 32;
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}
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#define CUDNN_IS_POW_2(x) (0 == ((x) & ((x) -1)))
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int32_t find_log_2(int32_t x, bool round_up = false)
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{
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int32_t a = 31 - clz(x);
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if (round_up)
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{
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a += !CUDNN_IS_POW_2(x);
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}
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return a;
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}
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void findDivisor(int32_t denom, uint32_t& mul_coeff, uint32_t& shift_coeff)
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{
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if (denom == 0)
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{
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return;
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}
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if (denom == 1)
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{
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// if dividing by 1, reduced math doesn't work because mul_coeff would
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// need to be 2^32, which doesn't fit into uint32_t. the div()
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// routine handles this special case separately.
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mul_coeff = 0;
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shift_coeff = 0;
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return;
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}
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// To express the division N/D in terms of a multiplication, what we first
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// imagine is simply N*(1/D). However, 1/D will always evaluate to 0 (for D>1),
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// so we need another way. There's nothing that says we have to use exactly
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// the fraction 1/D; instead it could be any X/Y that reduces to 1/D (i.e.,
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// Y=X*D), or at least to "close enough" to it. If we pick Y that is a power
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// of two, then the N*(X/Y) can be N*X followed by a right-shift by some amount.
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// The power of two we should pick should be at least 2^32, because in the
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// div() routine we'll use umulhi(), which returns only the upper 32 bits --
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// this being equivalent to a right-shift by 32. But we might want a higher
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// power of two for better accuracy depending on the magnitude of the denominator.
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// Once we've picked Y, then X [our mul_coeff value] is simply Y/D, rounding up,
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// and we save shift_coeff as whatever further shift we have to do beyond
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// what the umulhi() implies.
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uint32_t p = 31 + find_log_2(denom, true);
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uint32_t m = ((1ULL << p) + (uint32_t) denom - 1) / (uint32_t) denom;
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mul_coeff = m;
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shift_coeff = p - 32;
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}
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} // namespace nvinfer1::plugin::detail
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