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.
25 * $Id: bit_operations.h,v 1.11 2006/11/28 15:37:03 steveu Exp $
30 #if !defined(_BIT_OPERATIONS_H_)
31 #define _BIT_OPERATIONS_H_
33 #if defined(__i386__) || defined(__x86_64__)
34 /*! \brief Find the bit position of the highest set bit in a word
35 \param bits The word to be searched
36 \return The bit number of the highest set bit, or -1 if the word is zero. */
37 static __inline__ int top_bit(unsigned int bits)
41 __asm__(" xorl %[res],%[res];\n"
43 " bsrl %[bits],%[res]\n"
50 /*! \brief Find the bit position of the lowest set bit in a word
51 \param bits The word to be searched
52 \return The bit number of the lowest set bit, or -1 if the word is zero. */
53 static __inline__ int bottom_bit(unsigned int bits)
57 __asm__(" xorl %[res],%[res];\n"
59 " bsfl %[bits],%[res]\n"
66 static __inline__ int top_bit(unsigned int bits)
73 if (bits & 0xFFFF0000) {
77 if (bits & 0xFF00FF00) {
81 if (bits & 0xF0F0F0F0) {
85 if (bits & 0xCCCCCCCC) {
89 if (bits & 0xAAAAAAAA) {
96 static __inline__ int bottom_bit(unsigned int bits)
103 if (bits & 0x0000FFFF) {
107 if (bits & 0x00FF00FF) {
111 if (bits & 0x0F0F0F0F) {
115 if (bits & 0x33333333) {
119 if (bits & 0x55555555) {
127 /*! \brief Bit reverse a byte.
128 \param data The byte to be reversed.
129 \return The bit reversed version of data. */
130 static __inline__ uint8_t bit_reverse8(uint8_t x)
132 #if defined(__i386__) || defined(__x86_64__)
133 /* If multiply is fast */
134 return ((x * 0x0802U & 0x22110U) | (x * 0x8020U & 0x88440U)) *
137 /* If multiply is slow, but we have a barrel shifter */
138 x = (x >> 4) | (x << 4);
139 x = ((x & 0xCC) >> 2) | ((x & 0x33) << 2);
140 return ((x & 0xAA) >> 1) | ((x & 0x55) << 1);
144 /*! \brief Bit reverse a 16 bit word.
145 \param data The word to be reversed.
146 \return The bit reversed version of data. */
147 uint16_t bit_reverse16(uint16_t data);
149 /*! \brief Bit reverse a 32 bit word.
150 \param data The word to be reversed.
151 \return The bit reversed version of data. */
152 uint32_t bit_reverse32(uint32_t data);
154 /*! \brief Bit reverse each of the four bytes in a 32 bit word.
155 \param data The word to be reversed.
156 \return The bit reversed version of data. */
157 uint32_t bit_reverse_4bytes(uint32_t data);
159 /*! \brief Find the number of set bits in a 32 bit word.
160 \param x The word to be searched.
161 \return The number of set bits. */
162 int one_bits32(uint32_t x);
164 /*! \brief Create a mask as wide as the number in a 32 bit word.
165 \param x The word to be searched.
167 uint32_t make_mask32(uint32_t x);
169 /*! \brief Create a mask as wide as the number in a 16 bit word.
170 \param x The word to be searched.
172 uint16_t make_mask16(uint16_t x);
174 /*! \brief Find the least significant one in a word, and return a word
175 with just that bit set.
176 \param x The word to be searched.
177 \return The word with the single set bit. */
178 static __inline__ uint32_t least_significant_one32(uint32_t x)
180 return (x & (-(int32_t) x));
183 /*! \brief Find the most significant one in a word, and return a word
184 with just that bit set.
185 \param x The word to be searched.
186 \return The word with the single set bit. */
187 static __inline__ uint32_t most_significant_one32(uint32_t x)
189 #if defined(__i386__) || defined(__x86_64__)
190 return 1 << top_bit(x);
193 return (x ^ (x >> 1));
197 /*! \brief Find the parity of a byte.
198 \param x The byte to be checked.
199 \return 1 for odd, or 0 for even. */
200 static __inline__ int parity8(uint8_t x)
202 x = (x ^ (x >> 4)) & 0x0F;
203 return (0x6996 >> x) & 1;
206 /*! \brief Find the parity of a 16 bit word.
207 \param x The word to be checked.
208 \return 1 for odd, or 0 for even. */
209 static __inline__ int parity16(uint16_t x)
212 x = (x ^ (x >> 4)) & 0x0F;
213 return (0x6996 >> x) & 1;
216 /*! \brief Find the parity of a 32 bit word.
217 \param x The word to be checked.
218 \return 1 for odd, or 0 for even. */
219 static __inline__ int parity32(uint32_t x)
223 x = (x ^ (x >> 4)) & 0x0F;
224 return (0x6996 >> x) & 1;
228 /*- End of file ------------------------------------------------------------*/