ref: 69549ac05b071e450032fc149cd2a694166d337c
dir: /silk/silk_log2lin.c/
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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "silk_SigProc_FIX.h"
/* Approximation of 2^() (very close inverse of silk_lin2log()) */
/* Convert input to a linear scale */
opus_int32 silk_log2lin( const opus_int32 inLog_Q7 ) /* I: Input on log scale */
{
opus_int32 out, frac_Q7;
if( inLog_Q7 < 0 ) {
return 0;
}
out = SKP_LSHIFT( 1, SKP_RSHIFT( inLog_Q7, 7 ) );
frac_Q7 = inLog_Q7 & 0x7F;
if( inLog_Q7 < 2048 ) {
/* Piece-wise parabolic approximation */
out = SKP_ADD_RSHIFT( out, SKP_MUL( out, SKP_SMLAWB( frac_Q7, SKP_MUL( frac_Q7, 128 - frac_Q7 ), -174 ) ), 7 );
} else {
/* Piece-wise parabolic approximation */
out = SKP_MLA( out, SKP_RSHIFT( out, 7 ), SKP_SMLAWB( frac_Q7, SKP_MUL( frac_Q7, 128 - frac_Q7 ), -174 ) );
}
return out;
}