ref: 1a1736526d1421b682418c47801d967f2bdd0a70
dir: /silk/silk_sigm_Q15.c/
/***********************************************************************
Copyright (c) 2006-2011, Skype Limited. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, (subject to the limitations in the disclaimer below)
are permitted provided that the following conditions are met:
- Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
- Neither the name of Skype Limited, nor the names of specific
contributors, may be used to endorse or promote products derived from
this software without specific prior written permission.
NO EXPRESS OR IMPLIED LICENSES TO ANY PARTY'S PATENT RIGHTS ARE GRANTED
BY THIS LICENSE. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING,
BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
***********************************************************************/
/* Approximate sigmoid function */
#include "silk_SigProc_FIX.h"
/* fprintf(1, '%d, ', round(1024 * ([1 ./ (1 + exp(-(1:5))), 1] - 1 ./ (1 + exp(-(0:5)))))); */
static const SKP_int32 sigm_LUT_slope_Q10[ 6 ] = {
237, 153, 73, 30, 12, 7
};
/* fprintf(1, '%d, ', round(32767 * 1 ./ (1 + exp(-(0:5))))); */
static const SKP_int32 sigm_LUT_pos_Q15[ 6 ] = {
16384, 23955, 28861, 31213, 32178, 32548
};
/* fprintf(1, '%d, ', round(32767 * 1 ./ (1 + exp((0:5))))); */
static const SKP_int32 sigm_LUT_neg_Q15[ 6 ] = {
16384, 8812, 3906, 1554, 589, 219
};
SKP_int silk_sigm_Q15( SKP_int in_Q5 )
{
SKP_int ind;
if( in_Q5 < 0 ) {
/* Negative input */
in_Q5 = -in_Q5;
if( in_Q5 >= 6 * 32 ) {
return 0; /* Clip */
} else {
/* Linear interpolation of look up table */
ind = SKP_RSHIFT( in_Q5, 5 );
return( sigm_LUT_neg_Q15[ ind ] - SKP_SMULBB( sigm_LUT_slope_Q10[ ind ], in_Q5 & 0x1F ) );
}
} else {
/* Positive input */
if( in_Q5 >= 6 * 32 ) {
return 32767; /* clip */
} else {
/* Linear interpolation of look up table */
ind = SKP_RSHIFT( in_Q5, 5 );
return( sigm_LUT_pos_Q15[ ind ] + SKP_SMULBB( sigm_LUT_slope_Q10[ ind ], in_Q5 & 0x1F ) );
}
}
}