72 lines
2.0 KiB
C
72 lines
2.0 KiB
C
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// Tencent is pleased to support the open source community by making RapidJSON available.
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//
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// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
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//
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// Licensed under the MIT License (the "License"); you may not use this file except
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// in compliance with the License. You may obtain a copy of the License at
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//
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// http://opensource.org/licenses/MIT
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//
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// Unless required by applicable law or agreed to in writing, software distributed
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// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
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// CONDITIONS OF ANY KIND, either express or implied. See the License for the
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// specific language governing permissions and limitations under the License.
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#ifndef RAPIDJSON_CLZLL_H_
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#define RAPIDJSON_CLZLL_H_
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#include "../rapidjson.h"
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#if defined(_MSC_VER)
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#include <intrin.h>
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#if defined(_WIN64)
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#pragma intrinsic(_BitScanReverse64)
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#else
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#pragma intrinsic(_BitScanReverse)
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#endif
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#endif
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RAPIDJSON_NAMESPACE_BEGIN
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namespace internal {
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inline uint32_t clzll(uint64_t x) {
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// Passing 0 to __builtin_clzll is UB in GCC and results in an
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// infinite loop in the software implementation.
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RAPIDJSON_ASSERT(x != 0);
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#if defined(_MSC_VER)
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unsigned long r = 0;
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#if defined(_WIN64)
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_BitScanReverse64(&r, x);
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#else
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// Scan the high 32 bits.
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if (_BitScanReverse(&r, static_cast<uint32_t>(x >> 32)))
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return 63 - (r + 32);
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// Scan the low 32 bits.
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_BitScanReverse(&r, static_cast<uint32_t>(x & 0xFFFFFFFF));
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#endif // _WIN64
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return 63 - r;
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#elif (defined(__GNUC__) && __GNUC__ >= 4) || RAPIDJSON_HAS_BUILTIN(__builtin_clzll)
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// __builtin_clzll wrapper
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return static_cast<uint32_t>(__builtin_clzll(x));
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#else
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// naive version
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uint32_t r;
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while (!(x & (static_cast<uint64_t>(1) << 63))) {
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x <<= 1;
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++r;
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}
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return r;
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#endif // _MSC_VER
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}
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#define RAPIDJSON_CLZLL RAPIDJSON_NAMESPACE::internal::clzll
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} // namespace internal
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RAPIDJSON_NAMESPACE_END
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#endif // RAPIDJSON_CLZLL_H_
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