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1 /***********************************************************************
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2 Copyright (c) 2006-2011, Skype Limited. All rights reserved.
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3 Redistribution and use in source and binary forms, with or without
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4 modification, are permitted provided that the following conditions
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5 are met:
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6 - Redistributions of source code must retain the above copyright notice,
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7 this list of conditions and the following disclaimer.
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8 - Redistributions in binary form must reproduce the above copyright
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9 notice, this list of conditions and the following disclaimer in the
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10 documentation and/or other materials provided with the distribution.
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11 - Neither the name of Internet Society, IETF or IETF Trust, nor the
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12 names of specific contributors, may be used to endorse or promote
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13 products derived from this software without specific prior written
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14 permission.
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15 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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16 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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17 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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18 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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19 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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20 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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21 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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22 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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23 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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24 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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25 POSSIBILITY OF SUCH DAMAGE.
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26 ***********************************************************************/
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27
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28 #ifdef HAVE_CONFIG_H
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29 #include "config.h"
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30 #endif
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31
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32 #include "SigProc_FIX.h"
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33 #include "resampler_rom.h"
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34
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35 /* Downsample by a factor 2 */
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36 void silk_resampler_down2(
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37 opus_int32 *S, /* I/O State vector [ 2 ] */
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38 opus_int16 *out, /* O Output signal [ floor(len/2) ] */
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39 const opus_int16 *in, /* I Input signal [ len ] */
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40 opus_int32 inLen /* I Number of input samples */
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41 )
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42 {
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43 opus_int32 k, len2 = silk_RSHIFT32( inLen, 1 );
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44 opus_int32 in32, out32, Y, X;
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45
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46 celt_assert( silk_resampler_down2_0 > 0 );
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47 celt_assert( silk_resampler_down2_1 < 0 );
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48
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49 /* Internal variables and state are in Q10 format */
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50 for( k = 0; k < len2; k++ ) {
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51 /* Convert to Q10 */
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52 in32 = silk_LSHIFT( (opus_int32)in[ 2 * k ], 10 );
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53
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54 /* All-pass section for even input sample */
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55 Y = silk_SUB32( in32, S[ 0 ] );
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56 X = silk_SMLAWB( Y, Y, silk_resampler_down2_1 );
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57 out32 = silk_ADD32( S[ 0 ], X );
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58 S[ 0 ] = silk_ADD32( in32, X );
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59
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60 /* Convert to Q10 */
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61 in32 = silk_LSHIFT( (opus_int32)in[ 2 * k + 1 ], 10 );
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62
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63 /* All-pass section for odd input sample, and add to output of previous section */
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64 Y = silk_SUB32( in32, S[ 1 ] );
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65 X = silk_SMULWB( Y, silk_resampler_down2_0 );
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66 out32 = silk_ADD32( out32, S[ 1 ] );
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67 out32 = silk_ADD32( out32, X );
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68 S[ 1 ] = silk_ADD32( in32, X );
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69
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70 /* Add, convert back to int16 and store to output */
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71 out[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( out32, 11 ) );
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72 }
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73 }
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74
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