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"
45 : [bits] "rm" (bits));
49 /*! \brief Find the bit position of the lowest set bit in a word
50 \param bits The word to be searched
51 \return The bit number of the lowest set bit, or -1 if the word is zero. */
52 static __inline__ int bottom_bit(unsigned int bits)
56 __asm__ (" xorl %[res],%[res];\n"
58 " bsfl %[bits],%[res]\n"
60 : [bits] "rm" (bits));
64 static __inline__ int top_bit(unsigned int bits)
71 if (bits & 0xFFFF0000)
76 if (bits & 0xFF00FF00)
81 if (bits & 0xF0F0F0F0)
86 if (bits & 0xCCCCCCCC)
91 if (bits & 0xAAAAAAAA)
99 static __inline__ int bottom_bit(unsigned int bits)
106 if (bits & 0x0000FFFF)
111 if (bits & 0x00FF00FF)
116 if (bits & 0x0F0F0F0F)
121 if (bits & 0x33333333)
126 if (bits & 0x55555555)
135 /*! \brief Bit reverse a byte.
136 \param data The byte to be reversed.
137 \return The bit reversed version of data. */
138 static __inline__ uint8_t bit_reverse8(uint8_t x)
140 #if defined(__i386__) || defined(__x86_64__)
141 /* If multiply is fast */
142 return ((x*0x0802U & 0x22110U) | (x*0x8020U & 0x88440U))*0x10101U >> 16;
144 /* If multiply is slow, but we have a barrel shifter */
145 x = (x >> 4) | (x << 4);
146 x = ((x & 0xCC) >> 2) | ((x & 0x33) << 2);
147 return ((x & 0xAA) >> 1) | ((x & 0x55) << 1);
151 /*! \brief Bit reverse a 16 bit word.
152 \param data The word to be reversed.
153 \return The bit reversed version of data. */
154 uint16_t bit_reverse16(uint16_t data);
156 /*! \brief Bit reverse a 32 bit word.
157 \param data The word to be reversed.
158 \return The bit reversed version of data. */
159 uint32_t bit_reverse32(uint32_t data);
161 /*! \brief Bit reverse each of the four bytes in a 32 bit word.
162 \param data The word to be reversed.
163 \return The bit reversed version of data. */
164 uint32_t bit_reverse_4bytes(uint32_t data);
166 /*! \brief Find the number of set bits in a 32 bit word.
167 \param x The word to be searched.
168 \return The number of set bits. */
169 int one_bits32(uint32_t x);
171 /*! \brief Create a mask as wide as the number in a 32 bit word.
172 \param x The word to be searched.
174 uint32_t make_mask32(uint32_t x);
176 /*! \brief Create a mask as wide as the number in a 16 bit word.
177 \param x The word to be searched.
179 uint16_t make_mask16(uint16_t x);
181 /*! \brief Find the least 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 least_significant_one32(uint32_t x)
187 return (x & (-(int32_t) x));
190 /*! \brief Find the most significant one in a word, and return a word
191 with just that bit set.
192 \param x The word to be searched.
193 \return The word with the single set bit. */
194 static __inline__ uint32_t most_significant_one32(uint32_t x)
196 #if defined(__i386__) || defined(__x86_64__)
197 return 1 << top_bit(x);
200 return (x ^ (x >> 1));
204 /*! \brief Find the parity of a byte.
205 \param x The byte to be checked.
206 \return 1 for odd, or 0 for even. */
207 static __inline__ int parity8(uint8_t x)
209 x = (x ^ (x >> 4)) & 0x0F;
210 return (0x6996 >> x) & 1;
213 /*! \brief Find the parity of a 16 bit word.
214 \param x The word to be checked.
215 \return 1 for odd, or 0 for even. */
216 static __inline__ int parity16(uint16_t x)
219 x = (x ^ (x >> 4)) & 0x0F;
220 return (0x6996 >> x) & 1;
223 /*! \brief Find the parity of a 32 bit word.
224 \param x The word to be checked.
225 \return 1 for odd, or 0 for even. */
226 static __inline__ int parity32(uint32_t x)
230 x = (x ^ (x >> 4)) & 0x0F;
231 return (0x6996 >> x) & 1;
235 /*- End of file ------------------------------------------------------------*/