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     11 - Neither the name of Internet Society, IETF or IETF Trust, nor the
     12 names of specific contributors, may be used to endorse or promote
     13 products derived from this software without specific prior written
     14 permission.
     15 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
     16 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     17 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     18 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
     19 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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     21 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     22 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     23 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     24 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     25 POSSIBILITY OF SUCH DAMAGE.
     26 ***********************************************************************/
     27 
     28 #ifdef HAVE_CONFIG_H
     29 #include "config.h"
     30 #endif
     31 
     32 #include "SigProc_FIX.h"
     33 
     34 /* Coefficients for 2-band filter bank based on first-order allpass filters */
     35 static opus_int16 A_fb1_20 = 5394 << 1;
     36 static opus_int16 A_fb1_21 = -24290; /* (opus_int16)(20623 << 1) */
     37 
     38 /* Split signal into two decimated bands using first-order allpass filters */
     39 void silk_ana_filt_bank_1(
     40     const opus_int16            *in,                /* I    Input signal [N]                                            */
     41     opus_int32                  *S,                 /* I/O  State vector [2]                                            */
     42     opus_int16                  *outL,              /* O    Low band [N/2]                                              */
     43     opus_int16                  *outH,              /* O    High band [N/2]                                             */
     44     const opus_int32            N                   /* I    Number of input samples                                     */
     45 )
     46 {
     47     opus_int      k, N2 = silk_RSHIFT( N, 1 );
     48     opus_int32    in32, X, Y, out_1, out_2;
     49 
     50     /* Internal variables and state are in Q10 format */
     51     for( k = 0; k < N2; k++ ) {
     52         /* Convert to Q10 */
     53         in32 = silk_LSHIFT( (opus_int32)in[ 2 * k ], 10 );
     54 
     55         /* All-pass section for even input sample */
     56         Y      = silk_SUB32( in32, S[ 0 ] );
     57         X      = silk_SMLAWB( Y, Y, A_fb1_21 );
     58         out_1  = silk_ADD32( S[ 0 ], X );
     59         S[ 0 ] = silk_ADD32( in32, X );
     60 
     61         /* Convert to Q10 */
     62         in32 = silk_LSHIFT( (opus_int32)in[ 2 * k + 1 ], 10 );
     63 
     64         /* All-pass section for odd input sample, and add to output of previous section */
     65         Y      = silk_SUB32( in32, S[ 1 ] );
     66         X      = silk_SMULWB( Y, A_fb1_20 );
     67         out_2  = silk_ADD32( S[ 1 ], X );
     68         S[ 1 ] = silk_ADD32( in32, X );
     69 
     70         /* Add/subtract, convert back to int16 and store to output */
     71         outL[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( silk_ADD32( out_2, out_1 ), 11 ) );
     72         outH[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( silk_SUB32( out_2, out_1 ), 11 ) );
     73     }
     74 }
     75