1 // Copyright 2018 Google LLC
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 #ifndef ASTC_CODEC_BASE_MATH_UTILS_H_
16 #define ASTC_CODEC_BASE_MATH_UTILS_H_
17
18 #include "src/base/uint128.h"
19
20 #include <cassert>
21 #include <cstdint>
22 #include <type_traits>
23
24 namespace astc_codec {
25 namespace base {
26
Log2Floor(uint32_t n)27 inline int Log2Floor(uint32_t n) {
28 if (n == 0) {
29 return -1;
30 }
31
32 int log = 0;
33 uint32_t value = n;
34 for (int i = 4; i >= 0; --i) {
35 int shift = (1 << i);
36 uint32_t x = value >> shift;
37 if (x != 0) {
38 value = x;
39 log += shift;
40 }
41 }
42 assert(value == 1);
43 return log;
44 }
45
CountOnes(uint32_t n)46 inline int CountOnes(uint32_t n) {
47 n -= ((n >> 1) & 0x55555555);
48 n = ((n >> 2) & 0x33333333) + (n & 0x33333333);
49 return static_cast<int>((((n + (n >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24);
50 }
51
52 template<typename T>
ReverseBits(T value)53 inline T ReverseBits(T value) {
54 uint32_t s = sizeof(value) * 8;
55 T mask = ~T(0);
56 while ((s >>= 1) > 0) {
57 mask ^= (mask << s);
58 value = ((value >> s) & mask) | ((value << s) & ~mask);
59 }
60
61 return value;
62 }
63
64 template<typename T>
GetBits(T source,uint32_t offset,uint32_t count)65 inline T GetBits(T source, uint32_t offset, uint32_t count) {
66 static_assert(std::is_same<T, UInt128>::value || std::is_unsigned<T>::value,
67 "T must be unsigned.");
68
69 const uint32_t total_bits = sizeof(T) * 8;
70 assert(count > 0);
71 assert(offset + count <= total_bits);
72
73 const T mask = count == total_bits ? ~T(0) : ~T(0) >> (total_bits - count);
74 return (source >> offset) & mask;
75 }
76
77 } // namespace base
78 } // namespace astc_codec
79
80 #endif // ASTC_CODEC_BASE_MATH_UTILS_H_
81