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  /*                                                                      *
   * SKP_Silk_resampler_down2_3.c                                       *
   *                                                                      *
   * Downsample by a factor 2/3, low quality                              *
   *                                                                      *
   * Copyright 2010 (c), Skype Limited                                    *
   *                                                                      */
  
  #include "SKP_Silk_SigProc_FIX.h"
  #include "SKP_Silk_resampler_private.h"
  
  #define ORDER_FIR                   4
  
  /* Downsample by a factor 2/3, low quality */
  void SKP_Silk_resampler_down2_3(
      SKP_int32                           *S,         /* I/O: State vector [ 6 ]                  */
      SKP_int16                           *out,       /* O:   Output signal [ floor(2*inLen/3) ]  */
      const SKP_int16                     *in,        /* I:   Input signal [ inLen ]              */
      SKP_int32                           inLen       /* I:   Number of input samples             */
  )
  {
  	SKP_int32 nSamplesIn, counter, res_Q6;
  	SKP_int32 buf[ RESAMPLER_MAX_BATCH_SIZE_IN + ORDER_FIR ];
  	SKP_int32 *buf_ptr;
  
  	/* Copy buffered samples to start of buffer */
  	SKP_memcpy( buf, S, ORDER_FIR * sizeof( SKP_int32 ) );
  
  	/* Iterate over blocks of frameSizeIn input samples */
  	while( 1 ) {
  		nSamplesIn = SKP_min( inLen, RESAMPLER_MAX_BATCH_SIZE_IN );
  
  	    /* Second-order AR filter (output in Q8) */
  	    SKP_Silk_resampler_private_AR2( &S[ ORDER_FIR ], &buf[ ORDER_FIR ], in,
              SKP_Silk_Resampler_2_3_COEFS_LQ, nSamplesIn );
  
  		/* Interpolate filtered signal */
          buf_ptr = buf;
          counter = nSamplesIn;
          while( counter > 2 ) {
              /* Inner product */
  		    res_Q6 = SKP_SMULWB(         buf_ptr[ 0 ], SKP_Silk_Resampler_2_3_COEFS_LQ[ 2 ] );
  		    res_Q6 = SKP_SMLAWB( res_Q6, buf_ptr[ 1 ], SKP_Silk_Resampler_2_3_COEFS_LQ[ 3 ] );
  		    res_Q6 = SKP_SMLAWB( res_Q6, buf_ptr[ 2 ], SKP_Silk_Resampler_2_3_COEFS_LQ[ 5 ] );
  		    res_Q6 = SKP_SMLAWB( res_Q6, buf_ptr[ 3 ], SKP_Silk_Resampler_2_3_COEFS_LQ[ 4 ] );
  
              /* Scale down, saturate and store in output array */
              *out++ = (SKP_int16)SKP_SAT16( SKP_RSHIFT_ROUND( res_Q6, 6 ) );
  
  		    res_Q6 = SKP_SMULWB(         buf_ptr[ 1 ], SKP_Silk_Resampler_2_3_COEFS_LQ[ 4 ] );
  		    res_Q6 = SKP_SMLAWB( res_Q6, buf_ptr[ 2 ], SKP_Silk_Resampler_2_3_COEFS_LQ[ 5 ] );
  		    res_Q6 = SKP_SMLAWB( res_Q6, buf_ptr[ 3 ], SKP_Silk_Resampler_2_3_COEFS_LQ[ 3 ] );
  		    res_Q6 = SKP_SMLAWB( res_Q6, buf_ptr[ 4 ], SKP_Silk_Resampler_2_3_COEFS_LQ[ 2 ] );
  
              /* Scale down, saturate and store in output array */
              *out++ = (SKP_int16)SKP_SAT16( SKP_RSHIFT_ROUND( res_Q6, 6 ) );
  
              buf_ptr += 3;
              counter -= 3;
          }
  
  		in += nSamplesIn;
  		inLen -= nSamplesIn;
  
  		if( inLen > 0 ) {
  			/* More iterations to do; copy last part of filtered signal to beginning of buffer */
  			SKP_memcpy( buf, &buf[ nSamplesIn ], ORDER_FIR * sizeof( SKP_int32 ) );
  		} else {
  			break;
  		}
  	}
  
  	/* Copy last part of filtered signal to the state for the next call */
  	SKP_memcpy( S, &buf[ nSamplesIn ], ORDER_FIR * sizeof( SKP_int32 ) );
  }
  