opus/silk/sum_sqr_shift.c

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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "SigProc_FIX.h"

/* Compute number of bits to right shift the sum of squares of a vector */
/* of int16s to make it fit in an int32                                 */
void silk_sum_sqr_shift(
    opus_int32                  *energy,            /* O   Energy of x, after shifting to the right                     */
    opus_int                    *shift,             /* O   Number of bits right shift applied to energy                 */
    const opus_int16            *x,                 /* I   Input vector                                                 */
    opus_int                    len                 /* I   Length of input vector                                       */
)
{
    opus_int   i, shft;
    opus_int32 nrg_tmp, nrg;

    nrg  = 0;
    shft = 0;
    len--;
    for( i = 0; i < len; i += 2 ) {
        nrg = silk_SMLABB_ovflw( nrg, x[ i ], x[ i ] );
        nrg = silk_SMLABB_ovflw( nrg, x[ i + 1 ], x[ i + 1 ] );
        if( nrg < 0 ) {
            /* Scale down */
            nrg = (opus_int32)silk_RSHIFT_uint( (opus_uint32)nrg, 2 );
            shft = 2;
            break;
        }
    }
    for( ; i < len; i += 2 ) {
        nrg_tmp = silk_SMULBB( x[ i ], x[ i ] );
        nrg_tmp = silk_SMLABB_ovflw( nrg_tmp, x[ i + 1 ], x[ i + 1 ] );
        nrg = (opus_int32)silk_ADD_RSHIFT_uint( nrg, (opus_uint32)nrg_tmp, shft );
        if( nrg < 0 ) {
            /* Scale down */
            nrg = (opus_int32)silk_RSHIFT_uint( (opus_uint32)nrg, 2 );
            shft += 2;
        }
    }
    if( i == len ) {
        /* One sample left to process */
        nrg_tmp = silk_SMULBB( x[ i ], x[ i ] );
        nrg = (opus_int32)silk_ADD_RSHIFT_uint( nrg, nrg_tmp, shft );
    }

    /* Make sure to have at least one extra leading zero (two leading zeros in total) */
    if( nrg & 0xC0000000 ) {
        nrg = silk_RSHIFT_uint( (opus_uint32)nrg, 2 );
        shft += 2;
    }

    /* Output arguments */
    *shift  = shft;
    *energy = nrg;
}