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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 ) );
        }
    }
}

