/* Gain scalar quantization with hysteresis, uniform on log scale */
void silk_gains_quant(
opus_int8 ind[ MAX_NB_SUBFR ], /* O gain indices */
opus_int32 gain_Q16[ MAX_NB_SUBFR ], /* I/O gains (quantized out) */
opus_int8 *prev_ind, /* I/O last index in previous frame */
const opus_int conditional, /* I first gain is delta coded if 1 */
const opus_int nb_subfr /* I number of subframes */
)
{
opus_int k, double_step_size_threshold;
for( k = 0; k < nb_subfr; k++ ) {
/* Convert to log scale, scale, floor() */
ind[ k ] = silk_SMULWB( SCALE_Q16, silk_lin2log( gain_Q16[ k ] ) - OFFSET );
/* Round towards previous quantized gain (hysteresis) */
if( ind[ k ] < *prev_ind ) {
ind[ k ]++;
}
ind[ k ] = silk_LIMIT_int( ind[ k ], 0, N_LEVELS_QGAIN - 1 );
/* Compute delta indices and limit */
if( k == 0 && conditional == 0 ) {
/* Full index */
ind[ k ] = silk_LIMIT_int( ind[ k ], *prev_ind + MIN_DELTA_GAIN_QUANT, N_LEVELS_QGAIN - 1 );
*prev_ind = ind[ k ];
} else {
/* Delta index */
ind[ k ] = ind[ k ] - *prev_ind;
/* Double the quantization step size for large gain increases, so that the max gain level can be reached */
double_step_size_threshold = 2 * MAX_DELTA_GAIN_QUANT - N_LEVELS_QGAIN + *prev_ind;
if( ind[ k ] > double_step_size_threshold ) {
ind[ k ] = double_step_size_threshold + silk_RSHIFT( ind[ k ] - double_step_size_threshold + 1, 1 );
}
ind[ k ] = silk_LIMIT_int( ind[ k ], MIN_DELTA_GAIN_QUANT, MAX_DELTA_GAIN_QUANT );
/* Accumulate deltas */
if( ind[ k ] > double_step_size_threshold ) {
*prev_ind += silk_LSHIFT( ind[ k ], 1 ) - double_step_size_threshold;
*prev_ind = silk_min_int( *prev_ind, N_LEVELS_QGAIN - 1 );
} else {
*prev_ind += ind[ k ];
}
/* Shift to make non-negative */
ind[ k ] -= MIN_DELTA_GAIN_QUANT;
}
/* Scale and convert to linear scale */
gain_Q16[ k ] = silk_log2lin( silk_min_32( silk_SMULWB( INV_SCALE_Q16, *prev_ind ) + OFFSET, 3967 ) ); /* 3967 = 31 in Q7 */
}
}
/* Gains scalar dequantization, uniform on log scale */
void silk_gains_dequant(
opus_int32 gain_Q16[ MAX_NB_SUBFR ], /* O quantized gains */
const opus_int8 ind[ MAX_NB_SUBFR ], /* I gain indices */
opus_int8 *prev_ind, /* I/O last index in previous frame */
const opus_int conditional, /* I first gain is delta coded if 1 */
const opus_int nb_subfr /* I number of subframes */
)
{
opus_int k, ind_tmp, double_step_size_threshold;
for( k = 0; k < nb_subfr; k++ ) {
if( k == 0 && conditional == 0 ) {
/* Gain index is not allowed to go down more than 16 steps (~21.8 dB) */
*prev_ind = silk_max_int( ind[ k ], *prev_ind - 16 );
} else {
/* Delta index */
ind_tmp = ind[ k ] + MIN_DELTA_GAIN_QUANT;
/* Accumulate deltas */
double_step_size_threshold = 2 * MAX_DELTA_GAIN_QUANT - N_LEVELS_QGAIN + *prev_ind;
if( ind_tmp > double_step_size_threshold ) {
*prev_ind += silk_LSHIFT( ind_tmp, 1 ) - double_step_size_threshold;
} else {
*prev_ind += ind_tmp;
}
}
*prev_ind = silk_LIMIT_int( *prev_ind, 0, N_LEVELS_QGAIN - 1 );
/* Scale and convert to linear scale */
gain_Q16[ k ] = silk_log2lin( silk_min_32( silk_SMULWB( INV_SCALE_Q16, *prev_ind ) + OFFSET, 3967 ) ); /* 3967 = 31 in Q7 */
}
}
