ref: fe741259c1050baa5c828444dd5a968ed658d1fb
dir: /silk/SKP_Silk_sigm_Q15.c/
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/* *
* SKP_sigm_Q15.c *
* *
* Approximate sigmoid function *
* *
* Copyright 2006 (c), Skype Limited *
* Date: 060221 *
* */
#include "SKP_Silk_SigProc_FIX.h"
/********************************/
/* approximate sigmoid function */
/********************************/
/* 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 SKP_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 ) );
}
}
}