Replacing some 32x16 multiplies with 16x16 when both operands are 16 bits

silk/NLSF_del_dec_quant.c

@@ -46,8 +46,9 @@ opus_int32 silk_NLSF_del_dec_quant(                             /* O    Returns
 )
 {
     opus_int         i, j, nStates, ind_tmp, ind_min_max, ind_max_min, in_Q10, res_Q10;
-    opus_int         pred_Q10, diff_Q10, out0_Q10, out1_Q10, rate0_Q5, rate1_Q5;
-    opus_int32       RD_tmp_Q25, min_Q25, min_max_Q25, max_min_Q25, pred_coef_Q16;
+    opus_int         pred_Q10, diff_Q10, rate0_Q5, rate1_Q5;
+    opus_int16       out0_Q10, out1_Q10;
+    opus_int32       RD_tmp_Q25, min_Q25, min_max_Q25, max_min_Q25;
     opus_int         ind_sort[         NLSF_QUANT_DEL_DEC_STATES ];
     opus_int8        ind[              NLSF_QUANT_DEL_DEC_STATES ][ MAX_LPC_ORDER ];
     opus_int16       prev_out_Q10[ 2 * NLSF_QUANT_DEL_DEC_STATES ];
@@ -74,8 +75,8 @@ opus_int32 silk_NLSF_del_dec_quant(                             /* O    Returns
             out0_Q10 = silk_ADD16( out0_Q10, SILK_FIX_CONST( NLSF_QUANT_LEVEL_ADJ, 10 ) );
             out1_Q10 = silk_ADD16( out1_Q10, SILK_FIX_CONST( NLSF_QUANT_LEVEL_ADJ, 10 ) );
         }
-        out0_Q10_table[ i + NLSF_QUANT_MAX_AMPLITUDE_EXT ] = silk_SMULWB( (opus_int32)out0_Q10, quant_step_size_Q16 );
-        out1_Q10_table[ i + NLSF_QUANT_MAX_AMPLITUDE_EXT ] = silk_SMULWB( (opus_int32)out1_Q10, quant_step_size_Q16 );
+        out0_Q10_table[ i + NLSF_QUANT_MAX_AMPLITUDE_EXT ] = silk_RSHIFT( silk_SMULBB( out0_Q10, quant_step_size_Q16 ), 16 );
+        out1_Q10_table[ i + NLSF_QUANT_MAX_AMPLITUDE_EXT ] = silk_RSHIFT( silk_SMULBB( out1_Q10, quant_step_size_Q16 ), 16 );
     }
 
     silk_assert( (NLSF_QUANT_DEL_DEC_STATES & (NLSF_QUANT_DEL_DEC_STATES-1)) == 0 );     /* must be power of two */
@@ -85,12 +86,11 @@ opus_int32 silk_NLSF_del_dec_quant(                             /* O    Returns
     prev_out_Q10[ 0 ] = 0;
     for( i = order - 1; ; i-- ) {
         rates_Q5 = &ec_rates_Q5[ ec_ix[ i ] ];
-        pred_coef_Q16 = silk_LSHIFT( (opus_int32)pred_coef_Q8[ i ], 8 );
         in_Q10 = x_Q10[ i ];
         for( j = 0; j < nStates; j++ ) {
-            pred_Q10 = silk_SMULWB( pred_coef_Q16, prev_out_Q10[ j ] );
+            pred_Q10 = silk_RSHIFT( silk_SMULBB( (opus_int16)pred_coef_Q8[ i ], prev_out_Q10[ j ] ), 8 );
             res_Q10  = silk_SUB16( in_Q10, pred_Q10 );
-            ind_tmp  = silk_SMULWB( (opus_int32)inv_quant_step_size_Q6, res_Q10 );
+            ind_tmp  = silk_RSHIFT( silk_SMULBB( inv_quant_step_size_Q6, res_Q10 ), 16 );
             ind_tmp  = silk_LIMIT( ind_tmp, -NLSF_QUANT_MAX_AMPLITUDE_EXT, NLSF_QUANT_MAX_AMPLITUDE_EXT-1 );
             ind[ j ][ i ] = (opus_int8)ind_tmp;