clzll.h
1// Tencent is pleased to support the open source community by making RapidJSON available.
2//
3// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
4//
5// Licensed under the MIT License (the "License"); you may not use this file except
6// in compliance with the License. You may obtain a copy of the License at
7//
8// http://opensource.org/licenses/MIT
9//
10// Unless required by applicable law or agreed to in writing, software distributed
11// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
12// CONDITIONS OF ANY KIND, either express or implied. See the License for the
13// specific language governing permissions and limitations under the License.
14
15#ifndef RAPIDJSON_CLZLL_H_
16#define RAPIDJSON_CLZLL_H_
17
18#include "../rapidjson.h"
19
20#if defined(_MSC_VER)
21#include <intrin.h>
22#if defined(_WIN64)
23#pragma intrinsic(_BitScanReverse64)
24#else
25#pragma intrinsic(_BitScanReverse)
26#endif
27#endif
28
29RAPIDJSON_NAMESPACE_BEGIN
30namespace internal {
31
32#if (defined(__GNUC__) && __GNUC__ >= 4) || RAPIDJSON_HAS_BUILTIN(__builtin_clzll)
33#define RAPIDJSON_CLZLL __builtin_clzll
34#else
35
36inline uint32_t clzll(uint64_t x) {
37 // Passing 0 to __builtin_clzll is UB in GCC and results in an
38 // infinite loop in the software implementation.
39 RAPIDJSON_ASSERT(x != 0);
40
41#if defined(_MSC_VER)
42 unsigned long r = 0;
43#if defined(_WIN64)
44 _BitScanReverse64(&r, x);
45#else
46 // Scan the high 32 bits.
47 if (_BitScanReverse(&r, static_cast<uint32_t>(x >> 32)))
48 return 63 - (r + 32);
49
50 // Scan the low 32 bits.
51 _BitScanReverse(&r, static_cast<uint32_t>(x & 0xFFFFFFFF));
52#endif // _WIN64
53
54 return 63 - r;
55#else
56 uint32_t r;
57 while (!(x & (static_cast<uint64_t>(1) << 63))) {
58 x <<= 1;
59 ++r;
60 }
61
62 return r;
63#endif // _MSC_VER
64}
65
66#define RAPIDJSON_CLZLL RAPIDJSON_NAMESPACE::internal::clzll
67#endif // (defined(__GNUC__) && __GNUC__ >= 4) || RAPIDJSON_HAS_BUILTIN(__builtin_clzll)
68
69} // namespace internal
70RAPIDJSON_NAMESPACE_END
71
72#endif // RAPIDJSON_CLZLL_H_
#define RAPIDJSON_ASSERT(x)
Assertion.
Definition: rapidjson.h:406