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27
28 #ifdef HAVE_CONFIG_H
29 #include "config.h"
30 #endif
31
32 #include "SigProc_FIX.h"
33
34 /* Approximation of 2^() (very close inverse of silk_lin2log()) */
35 /* Convert input to a linear scale */
silk_log2lin(const opus_int32 inLog_Q7)36 opus_int32 silk_log2lin(
37 const opus_int32 inLog_Q7 /* I input on log scale */
38 )
39 {
40 opus_int32 out, frac_Q7;
41
42 if( inLog_Q7 < 0 ) {
43 return 0;
44 } else if ( inLog_Q7 >= 3967 ) {
45 return silk_int32_MAX;
46 }
47
48 out = silk_LSHIFT( 1, silk_RSHIFT( inLog_Q7, 7 ) );
49 frac_Q7 = inLog_Q7 & 0x7F;
50 if( inLog_Q7 < 2048 ) {
51 /* Piece-wise parabolic approximation */
52 out = silk_ADD_RSHIFT32( out, silk_MUL( out, silk_SMLAWB( frac_Q7, silk_SMULBB( frac_Q7, 128 - frac_Q7 ), -174 ) ), 7 );
53 } else {
54 /* Piece-wise parabolic approximation */
55 out = silk_MLA( out, silk_RSHIFT( out, 7 ), silk_SMLAWB( frac_Q7, silk_SMULBB( frac_Q7, 128 - frac_Q7 ), -174 ) );
56 }
57 return out;
58 }
59