ref: d77d6a58fcfaeb480c705d2242a4f654cb3aa57f
dir: /silk/silk_schur.c/
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#include "silk_SigProc_FIX.h"
/* Faster than schur64(), but much less accurate. */
/* uses SMLAWB(), requiring armv5E and higher. */
SKP_int32 silk_schur( /* O: Returns residual energy */
SKP_int16 *rc_Q15, /* O: reflection coefficients [order] Q15 */
const SKP_int32 *c, /* I: correlations [order+1] */
const SKP_int32 order /* I: prediction order */
)
{
SKP_int k, n, lz;
SKP_int32 C[ SILK_MAX_ORDER_LPC + 1 ][ 2 ];
SKP_int32 Ctmp1, Ctmp2, rc_tmp_Q15;
/* Get number of leading zeros */
lz = silk_CLZ32( c[ 0 ] );
/* Copy correlations and adjust level to Q30 */
if( lz < 2 ) {
/* lz must be 1, so shift one to the right */
for( k = 0; k < order + 1; k++ ) {
C[ k ][ 0 ] = C[ k ][ 1 ] = SKP_RSHIFT( c[ k ], 1 );
}
} else if( lz > 2 ) {
/* Shift to the left */
lz -= 2;
for( k = 0; k < order + 1; k++ ) {
C[ k ][ 0 ] = C[ k ][ 1 ] = SKP_LSHIFT( c[ k ], lz );
}
} else {
/* No need to shift */
for( k = 0; k < order + 1; k++ ) {
C[ k ][ 0 ] = C[ k ][ 1 ] = c[ k ];
}
}
for( k = 0; k < order; k++ ) {
/* Get reflection coefficient */
rc_tmp_Q15 = -SKP_DIV32_16( C[ k + 1 ][ 0 ], SKP_max_32( SKP_RSHIFT( C[ 0 ][ 1 ], 15 ), 1 ) );
/* Clip (shouldn't happen for properly conditioned inputs) */
rc_tmp_Q15 = SKP_SAT16( rc_tmp_Q15 );
/* Store */
rc_Q15[ k ] = ( SKP_int16 )rc_tmp_Q15;
/* Update correlations */
for( n = 0; n < order - k; n++ ) {
Ctmp1 = C[ n + k + 1 ][ 0 ];
Ctmp2 = C[ n ][ 1 ];
C[ n + k + 1 ][ 0 ] = SKP_SMLAWB( Ctmp1, SKP_LSHIFT( Ctmp2, 1 ), rc_tmp_Q15 );
C[ n ][ 1 ] = SKP_SMLAWB( Ctmp2, SKP_LSHIFT( Ctmp1, 1 ), rc_tmp_Q15 );
}
}
/* return residual energy */
return C[ 0 ][ 1 ];
}