q3rally/engine/code/opus-1.2.1/silk/lin2log.c

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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "SigProc_FIX.h"
/* Approximation of 128 * log2() (very close inverse of silk_log2lin()) */
/* Convert input to a log scale    */
opus_int32 silk_lin2log(
    const opus_int32            inLin               /* I  input in linear scale                                         */
)
{
    opus_int32 lz, frac_Q7;

    silk_CLZ_FRAC( inLin, &lz, &frac_Q7 );

    /* Piece-wise parabolic approximation */
    return silk_ADD_LSHIFT32( silk_SMLAWB( frac_Q7, silk_MUL( frac_Q7, 128 - frac_Q7 ), 179 ), 31 - lz, 7 );
}