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68 lines
3.4 KiB
C
68 lines
3.4 KiB
C
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/***********************************************************************
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Copyright (c) 2006-2012, Skype Limited. All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, (subject to the limitations in the disclaimer below)
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are permitted provided that the following conditions are met:
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- Redistributions of source code must retain the above copyright notice,
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this list of conditions and the following disclaimer.
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- Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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- Neither the name of Skype Limited, nor the names of specific
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contributors, may be used to endorse or promote products derived from
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this software without specific prior written permission.
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NO EXPRESS OR IMPLIED LICENSES TO ANY PARTY'S PATENT RIGHTS ARE GRANTED
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BY THIS LICENSE. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING,
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BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
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ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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***********************************************************************/
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/* *
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* SKP_Silk_decimate2_coarsest.c *
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* *
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* downsample by a factor 2, coarsest *
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* */
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#include "SKP_Silk_SigProc_FLP.h"
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/* coefficients for coarsest 2-fold resampling */
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/* note that these differ from the interpolator with the same filter orders! */
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static float A20cst_FLP[ 1 ] = {0.289001464843750f};
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static float A21cst_FLP[ 1 ] = {0.780487060546875f};
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/* downsample by a factor 2, coarsest */
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void SKP_Silk_decimate2_coarsest_FLP(
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const SKP_float *in, /* I: 16 kHz signal [2*len] */
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SKP_float *S, /* I/O: state vector [2] */
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SKP_float *out, /* O: 8 kHz signal [len] */
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SKP_float *scratch, /* I: scratch memory [3*len] */
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const SKP_int32 len /* I: number of OUTPUT samples */
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)
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{
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SKP_int32 k;
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/* de-interleave allpass inputs */
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for ( k = 0; k < len; k++ ) {
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scratch[ k ] = in[ 2 * k + 0 ];
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scratch[ k + len ] = in[ 2 * k + 1 ];
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}
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/* allpass filters */
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SKP_Silk_allpass_int_FLP( scratch, S + 0, A21cst_FLP[ 0 ], scratch + 2 * len, len );
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SKP_Silk_allpass_int_FLP( scratch + len, S + 1, A20cst_FLP[ 0 ], scratch, len );
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/* add two allpass outputs */
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for ( k = 0; k < len; k++ ) {
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out[ k ] = 0.5f * ( scratch[ k ] + scratch[ k + 2 * len ] );
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}
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}
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