log_tabl.h revision 2f8ec03aa4809cec2b0944ca9bf1c7783e11b4ae 
1/*---------------------------------------------------------------------------*
2 *  log_tabl.h  *
3 *                                                                           *
4 *  Copyright 2007, 2008 Nuance Communciations, Inc.                               *
5 *                                                                           *
6 *  Licensed under the Apache License, Version 2.0 (the 'License');          *
7 *  you may not use this file except in compliance with the License.         *
8 *                                                                           *
9 *  You may obtain a copy of the License at                                  *
10 *      http://www.apache.org/licenses/LICENSE-2.0                           *
11 *                                                                           *
12 *  Unless required by applicable law or agreed to in writing, software      *
13 *  distributed under the License is distributed on an 'AS IS' BASIS,        *
14 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. *
15 *  See the License for the specific language governing permissions and      *
16 *  limitations under the License.                                           *
17 *                                                                           *
18 *---------------------------------------------------------------------------*/
19
20#ifndef _h_log_tabl_
21#define _h_log_tabl_
22
23#define LOG_SCALE 1024  /* smallest scale is about 0.1 dB */
24#define LOG_SCALE_SHIFT   10
25
26/**
27 * @todo document
28 */
29typedef struct
30{
31  int    size;
32  int    shift;
33  int    scale;
34  unsigned long mask;
35  const int *table;
36}
37log_table_info;
38
39void create_lookup_log(log_table_info *logtab, int num_bits);
40int log_lookup(log_table_info *logtab, int operand, int shift);
41int inv_log_lookup(log_table_info *logtab, int operand);
42void destroy_lookup_log(log_table_info *logtab);
43int integer_square_root(int operand);
44
45
46
47#endif
48