2 * SpanDSP - a series of DSP components for telephony
4 * bit_operations.h - Various bit level operations, such as bit reversal
6 * Written by Steve Underwood <steveu@coppice.org>
8 * Copyright (C) 2006 Steve Underwood
10 * All rights reserved.
12 * This program is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU General Public License version 2, as
14 * published by the Free Software Foundation.
16 * This program is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU General Public License for more details.
21 * You should have received a copy of the GNU General Public License
22 * along with this program; if not, write to the Free Software
23 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
28 #if !defined(_BIT_OPERATIONS_H_)
29 #define _BIT_OPERATIONS_H_
31 #if defined(__i386__) || defined(__x86_64__)
32 /*! \brief Find the bit position of the highest set bit in a word
33 \param bits The word to be searched
34 \return The bit number of the highest set bit, or -1 if the word is zero. */
35 static inline int top_bit(unsigned int bits)
39 __asm__(" xorl %[res],%[res];\n"
41 " bsrl %[bits],%[res]\n"
48 /*! \brief Find the bit position of the lowest set bit in a word
49 \param bits The word to be searched
50 \return The bit number of the lowest set bit, or -1 if the word is zero. */
51 static inline int bottom_bit(unsigned int bits)
55 __asm__(" xorl %[res],%[res];\n"
57 " bsfl %[bits],%[res]\n"
64 static inline int top_bit(unsigned int bits)
71 if (bits & 0xFFFF0000) {
75 if (bits & 0xFF00FF00) {
79 if (bits & 0xF0F0F0F0) {
83 if (bits & 0xCCCCCCCC) {
87 if (bits & 0xAAAAAAAA) {
94 static inline int bottom_bit(unsigned int bits)
101 if (bits & 0x0000FFFF) {
105 if (bits & 0x00FF00FF) {
109 if (bits & 0x0F0F0F0F) {
113 if (bits & 0x33333333) {
117 if (bits & 0x55555555) {
125 /*! \brief Bit reverse a byte.
126 \param data The byte to be reversed.
127 \return The bit reversed version of data. */
128 static inline uint8_t bit_reverse8(uint8_t x)
130 #if defined(__i386__) || defined(__x86_64__)
131 /* If multiply is fast */
132 return ((x * 0x0802U & 0x22110U) | (x * 0x8020U & 0x88440U)) *
135 /* If multiply is slow, but we have a barrel shifter */
136 x = (x >> 4) | (x << 4);
137 x = ((x & 0xCC) >> 2) | ((x & 0x33) << 2);
138 return ((x & 0xAA) >> 1) | ((x & 0x55) << 1);
142 /*! \brief Bit reverse a 16 bit word.
143 \param data The word to be reversed.
144 \return The bit reversed version of data. */
145 uint16_t bit_reverse16(uint16_t data);
147 /*! \brief Bit reverse a 32 bit word.
148 \param data The word to be reversed.
149 \return The bit reversed version of data. */
150 uint32_t bit_reverse32(uint32_t data);
152 /*! \brief Bit reverse each of the four bytes in a 32 bit word.
153 \param data The word to be reversed.
154 \return The bit reversed version of data. */
155 uint32_t bit_reverse_4bytes(uint32_t data);
157 /*! \brief Find the number of set bits in a 32 bit word.
158 \param x The word to be searched.
159 \return The number of set bits. */
160 int one_bits32(uint32_t x);
162 /*! \brief Create a mask as wide as the number in a 32 bit word.
163 \param x The word to be searched.
165 uint32_t make_mask32(uint32_t x);
167 /*! \brief Create a mask as wide as the number in a 16 bit word.
168 \param x The word to be searched.
170 uint16_t make_mask16(uint16_t x);
172 /*! \brief Find the least significant one in a word, and return a word
173 with just that bit set.
174 \param x The word to be searched.
175 \return The word with the single set bit. */
176 static inline uint32_t least_significant_one32(uint32_t x)
178 return x & (-(int32_t) x);
181 /*! \brief Find the most significant one in a word, and return a word
182 with just that bit set.
183 \param x The word to be searched.
184 \return The word with the single set bit. */
185 static inline uint32_t most_significant_one32(uint32_t x)
187 #if defined(__i386__) || defined(__x86_64__)
188 return 1 << top_bit(x);
195 /*! \brief Find the parity of a byte.
196 \param x The byte to be checked.
197 \return 1 for odd, or 0 for even. */
198 static inline int parity8(uint8_t x)
200 x = (x ^ (x >> 4)) & 0x0F;
201 return (0x6996 >> x) & 1;
204 /*! \brief Find the parity of a 16 bit word.
205 \param x The word to be checked.
206 \return 1 for odd, or 0 for even. */
207 static inline int parity16(uint16_t x)
210 x = (x ^ (x >> 4)) & 0x0F;
211 return (0x6996 >> x) & 1;
214 /*! \brief Find the parity of a 32 bit word.
215 \param x The word to be checked.
216 \return 1 for odd, or 0 for even. */
217 static inline int parity32(uint32_t x)
221 x = (x ^ (x >> 4)) & 0x0F;
222 return (0x6996 >> x) & 1;
226 /*- End of file ------------------------------------------------------------*/