1 /* SPDX-License-Identifier: GPL-2.0+ OR BSD-3-Clause */
2 /*
3 * Copyright (c) Meta Platforms, Inc. and affiliates.
4 * All rights reserved.
5 *
6 * This source code is licensed under both the BSD-style license (found in the
7 * LICENSE file in the root directory of this source tree) and the GPLv2 (found
8 * in the COPYING file in the root directory of this source tree).
9 * You may select, at your option, one of the above-listed licenses.
10 */
11
12 #ifndef ZSTD_BITS_H
13 #define ZSTD_BITS_H
14
15 #include "mem.h"
16
ZSTD_countTrailingZeros32_fallback(U32 val)17 MEM_STATIC unsigned ZSTD_countTrailingZeros32_fallback(U32 val)
18 {
19 assert(val != 0);
20 {
21 static const U32 DeBruijnBytePos[32] = {0, 1, 28, 2, 29, 14, 24, 3,
22 30, 22, 20, 15, 25, 17, 4, 8,
23 31, 27, 13, 23, 21, 19, 16, 7,
24 26, 12, 18, 6, 11, 5, 10, 9};
25 return DeBruijnBytePos[((U32) ((val & -(S32) val) * 0x077CB531U)) >> 27];
26 }
27 }
28
ZSTD_countTrailingZeros32(U32 val)29 MEM_STATIC unsigned ZSTD_countTrailingZeros32(U32 val)
30 {
31 assert(val != 0);
32 #if (__GNUC__ >= 4)
33 return (unsigned)__builtin_ctz(val);
34 #else
35 return ZSTD_countTrailingZeros32_fallback(val);
36 #endif
37 }
38
ZSTD_countLeadingZeros32_fallback(U32 val)39 MEM_STATIC unsigned ZSTD_countLeadingZeros32_fallback(U32 val)
40 {
41 assert(val != 0);
42 {
43 static const U32 DeBruijnClz[32] = {0, 9, 1, 10, 13, 21, 2, 29,
44 11, 14, 16, 18, 22, 25, 3, 30,
45 8, 12, 20, 28, 15, 17, 24, 7,
46 19, 27, 23, 6, 26, 5, 4, 31};
47 val |= val >> 1;
48 val |= val >> 2;
49 val |= val >> 4;
50 val |= val >> 8;
51 val |= val >> 16;
52 return 31 - DeBruijnClz[(val * 0x07C4ACDDU) >> 27];
53 }
54 }
55
ZSTD_countLeadingZeros32(U32 val)56 MEM_STATIC unsigned ZSTD_countLeadingZeros32(U32 val)
57 {
58 assert(val != 0);
59 #if (__GNUC__ >= 4)
60 return (unsigned)__builtin_clz(val);
61 #else
62 return ZSTD_countLeadingZeros32_fallback(val);
63 #endif
64 }
65
ZSTD_countTrailingZeros64(U64 val)66 MEM_STATIC unsigned ZSTD_countTrailingZeros64(U64 val)
67 {
68 assert(val != 0);
69 #if (__GNUC__ >= 4) && defined(__LP64__)
70 return (unsigned)__builtin_ctzll(val);
71 #else
72 {
73 U32 mostSignificantWord = (U32)(val >> 32);
74 U32 leastSignificantWord = (U32)val;
75 if (leastSignificantWord == 0) {
76 return 32 + ZSTD_countTrailingZeros32(mostSignificantWord);
77 } else {
78 return ZSTD_countTrailingZeros32(leastSignificantWord);
79 }
80 }
81 #endif
82 }
83
ZSTD_countLeadingZeros64(U64 val)84 MEM_STATIC unsigned ZSTD_countLeadingZeros64(U64 val)
85 {
86 assert(val != 0);
87 #if (__GNUC__ >= 4)
88 return (unsigned)(__builtin_clzll(val));
89 #else
90 {
91 U32 mostSignificantWord = (U32)(val >> 32);
92 U32 leastSignificantWord = (U32)val;
93 if (mostSignificantWord == 0) {
94 return 32 + ZSTD_countLeadingZeros32(leastSignificantWord);
95 } else {
96 return ZSTD_countLeadingZeros32(mostSignificantWord);
97 }
98 }
99 #endif
100 }
101
ZSTD_NbCommonBytes(size_t val)102 MEM_STATIC unsigned ZSTD_NbCommonBytes(size_t val)
103 {
104 if (MEM_isLittleEndian()) {
105 if (MEM_64bits()) {
106 return ZSTD_countTrailingZeros64((U64)val) >> 3;
107 } else {
108 return ZSTD_countTrailingZeros32((U32)val) >> 3;
109 }
110 } else { /* Big Endian CPU */
111 if (MEM_64bits()) {
112 return ZSTD_countLeadingZeros64((U64)val) >> 3;
113 } else {
114 return ZSTD_countLeadingZeros32((U32)val) >> 3;
115 }
116 }
117 }
118
ZSTD_highbit32(U32 val)119 MEM_STATIC unsigned ZSTD_highbit32(U32 val) /* compress, dictBuilder, decodeCorpus */
120 {
121 assert(val != 0);
122 return 31 - ZSTD_countLeadingZeros32(val);
123 }
124
125 /* ZSTD_rotateRight_*():
126 * Rotates a bitfield to the right by "count" bits.
127 * https://en.wikipedia.org/w/index.php?title=Circular_shift&oldid=991635599#Implementing_circular_shifts
128 */
129 MEM_STATIC
ZSTD_rotateRight_U64(U64 const value,U32 count)130 U64 ZSTD_rotateRight_U64(U64 const value, U32 count) {
131 assert(count < 64);
132 count &= 0x3F; /* for fickle pattern recognition */
133 return (value >> count) | (U64)(value << ((0U - count) & 0x3F));
134 }
135
136 MEM_STATIC
ZSTD_rotateRight_U32(U32 const value,U32 count)137 U32 ZSTD_rotateRight_U32(U32 const value, U32 count) {
138 assert(count < 32);
139 count &= 0x1F; /* for fickle pattern recognition */
140 return (value >> count) | (U32)(value << ((0U - count) & 0x1F));
141 }
142
143 MEM_STATIC
ZSTD_rotateRight_U16(U16 const value,U32 count)144 U16 ZSTD_rotateRight_U16(U16 const value, U32 count) {
145 assert(count < 16);
146 count &= 0x0F; /* for fickle pattern recognition */
147 return (value >> count) | (U16)(value << ((0U - count) & 0x0F));
148 }
149
150 #endif /* ZSTD_BITS_H */
151