1*a58d3d2aSXin Li /***********************************************************************
2*a58d3d2aSXin Li Copyright (c) 2006-2011, Skype Limited. All rights reserved.
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7*a58d3d2aSXin Li this list of conditions and the following disclaimer.
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15*a58d3d2aSXin Li THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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26*a58d3d2aSXin Li ***********************************************************************/
27*a58d3d2aSXin Li
28*a58d3d2aSXin Li #ifdef HAVE_CONFIG_H
29*a58d3d2aSXin Li #include "config.h"
30*a58d3d2aSXin Li #endif
31*a58d3d2aSXin Li
32*a58d3d2aSXin Li #include "SigProc_FIX.h"
33*a58d3d2aSXin Li
34*a58d3d2aSXin Li /* Approximation of 2^() (very close inverse of silk_lin2log()) */
35*a58d3d2aSXin Li /* Convert input to a linear scale */
silk_log2lin(const opus_int32 inLog_Q7)36*a58d3d2aSXin Li opus_int32 silk_log2lin(
37*a58d3d2aSXin Li const opus_int32 inLog_Q7 /* I input on log scale */
38*a58d3d2aSXin Li )
39*a58d3d2aSXin Li {
40*a58d3d2aSXin Li opus_int32 out, frac_Q7;
41*a58d3d2aSXin Li
42*a58d3d2aSXin Li if( inLog_Q7 < 0 ) {
43*a58d3d2aSXin Li return 0;
44*a58d3d2aSXin Li } else if ( inLog_Q7 >= 3967 ) {
45*a58d3d2aSXin Li return silk_int32_MAX;
46*a58d3d2aSXin Li }
47*a58d3d2aSXin Li
48*a58d3d2aSXin Li out = silk_LSHIFT( 1, silk_RSHIFT( inLog_Q7, 7 ) );
49*a58d3d2aSXin Li frac_Q7 = inLog_Q7 & 0x7F;
50*a58d3d2aSXin Li if( inLog_Q7 < 2048 ) {
51*a58d3d2aSXin Li /* Piece-wise parabolic approximation */
52*a58d3d2aSXin Li out = silk_ADD_RSHIFT32( out, silk_MUL( out, silk_SMLAWB( frac_Q7, silk_SMULBB( frac_Q7, 128 - frac_Q7 ), -174 ) ), 7 );
53*a58d3d2aSXin Li } else {
54*a58d3d2aSXin Li /* Piece-wise parabolic approximation */
55*a58d3d2aSXin Li out = silk_MLA( out, silk_RSHIFT( out, 7 ), silk_SMLAWB( frac_Q7, silk_SMULBB( frac_Q7, 128 - frac_Q7 ), -174 ) );
56*a58d3d2aSXin Li }
57*a58d3d2aSXin Li return out;
58*a58d3d2aSXin Li }
59