79 lines
3.8 KiB
C
79 lines
3.8 KiB
C
/***********************************************************************
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Copyright (c) 2006-2010, Skype Limited. All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, (subject to the limitations in the disclaimer below)
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are permitted provided that the following conditions are met:
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- Redistributions of source code must retain the above copyright notice,
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this list of conditions and the following disclaimer.
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- Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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- Neither the name of Skype Limited, nor the names of specific
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contributors, may be used to endorse or promote products derived from
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this software without specific prior written permission.
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NO EXPRESS OR IMPLIED LICENSES TO ANY PARTY'S PATENT RIGHTS ARE GRANTED
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BY THIS LICENSE. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING,
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BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
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ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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***********************************************************************/
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/* *
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* SKP_sigm_Q15.c *
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* *
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* Approximate sigmoid function *
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* *
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* Copyright 2006 (c), Skype Limited *
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* Date: 060221 *
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* */
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#include "SKP_Silk_SigProc_FIX.h"
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/********************************/
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/* approximate sigmoid function */
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/********************************/
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/* fprintf(1, '%d, ', round(1024 * ([1 ./ (1 + exp(-(1:5))), 1] - 1 ./ (1 + exp(-(0:5)))))); */
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static const SKP_int32 sigm_LUT_slope_Q10[ 6 ] = {
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237, 153, 73, 30, 12, 7
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};
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/* fprintf(1, '%d, ', round(32767 * 1 ./ (1 + exp(-(0:5))))); */
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static const SKP_int32 sigm_LUT_pos_Q15[ 6 ] = {
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16384, 23955, 28861, 31213, 32178, 32548
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};
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/* fprintf(1, '%d, ', round(32767 * 1 ./ (1 + exp((0:5))))); */
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static const SKP_int32 sigm_LUT_neg_Q15[ 6 ] = {
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16384, 8812, 3906, 1554, 589, 219
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};
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SKP_int SKP_Silk_sigm_Q15( SKP_int in_Q5 )
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{
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SKP_int ind;
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if( in_Q5 < 0 ) {
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/* Negative input */
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in_Q5 = -in_Q5;
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if( in_Q5 >= 6 * 32 ) {
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return 0; /* Clip */
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} else {
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/* Linear interpolation of look up table */
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ind = SKP_RSHIFT( in_Q5, 5 );
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return( sigm_LUT_neg_Q15[ ind ] - SKP_SMULBB( sigm_LUT_slope_Q10[ ind ], in_Q5 & 0x1F ) );
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}
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} else {
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/* Positive input */
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if( in_Q5 >= 6 * 32 ) {
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return 32767; /* clip */
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} else {
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/* Linear interpolation of look up table */
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ind = SKP_RSHIFT( in_Q5, 5 );
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return( sigm_LUT_pos_Q15[ ind ] + SKP_SMULBB( sigm_LUT_slope_Q10[ ind ], in_Q5 & 0x1F ) );
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}
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}
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}
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