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https://github.com/FFmpeg/FFmpeg.git
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Split exponent processing into separate functions.
Originally committed as revision 25991 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles
parent
0a0a8500fb
commit
dfdf73eb1a
@ -411,6 +411,41 @@ static void apply_mdct(AC3EncodeContext *s,
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}
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/**
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* Extract exponents from the MDCT coefficients.
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* This takes into account the normalization that was done to the input samples
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* by adjusting the exponents by the exponent shift values.
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*/
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static void extract_exponents(AC3EncodeContext *s,
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int32_t mdct_coef[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS],
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int8_t exp_shift[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS],
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uint8_t exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS])
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{
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int blk, ch, i;
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/* extract exponents */
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for (ch = 0; ch < s->channels; ch++) {
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for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
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/* compute "exponents". We take into account the normalization there */
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for (i = 0; i < AC3_MAX_COEFS; i++) {
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int e;
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int v = abs(mdct_coef[blk][ch][i]);
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if (v == 0)
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e = 24;
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else {
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e = 23 - av_log2(v) + exp_shift[blk][ch];
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if (e >= 24) {
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e = 24;
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mdct_coef[blk][ch][i] = 0;
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}
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}
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exp[blk][ch][i] = e;
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}
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}
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}
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}
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/**
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* Calculate the sum of absolute differences (SAD) between 2 sets of exponents.
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*/
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@ -472,6 +507,21 @@ static void compute_exp_strategy_ch(uint8_t exp_strategy[AC3_MAX_BLOCKS][AC3_MAX
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}
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/**
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* Calculate exponent strategies for all channels.
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*/
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static void compute_exp_strategy(AC3EncodeContext *s,
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uint8_t exp_strategy[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS],
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uint8_t exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS])
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{
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int ch;
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for (ch = 0; ch < s->channels; ch++) {
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compute_exp_strategy_ch(exp_strategy, exp, ch, ch == s->lfe_channel);
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}
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}
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/**
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* Set each encoded exponent in a block to the minimum of itself and the
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* exponent in the same frequency bin of a following block.
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@ -539,6 +589,68 @@ static int encode_exponents_blk_ch(uint8_t encoded_exp[AC3_MAX_COEFS],
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}
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/**
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* Encode exponents from original extracted form to what the decoder will see.
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* This copies and groups exponents based on exponent strategy and reduces
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* deltas between adjacent exponent groups so that they can be differentially
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* encoded.
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* @return bits needed to encode the exponents
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*/
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static int encode_exponents(AC3EncodeContext *s,
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uint8_t exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS],
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uint8_t exp_strategy[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS],
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uint8_t encoded_exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS])
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{
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int blk, blk1, blk2, ch;
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int frame_bits;
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frame_bits = 0;
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for (ch = 0; ch < s->channels; ch++) {
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/* for the EXP_REUSE case we select the min of the exponents */
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blk = 0;
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while (blk < AC3_MAX_BLOCKS) {
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blk1 = blk + 1;
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while (blk1 < AC3_MAX_BLOCKS && exp_strategy[blk1][ch] == EXP_REUSE) {
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exponent_min(exp[blk][ch], exp[blk1][ch], s->nb_coefs[ch]);
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blk1++;
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}
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frame_bits += encode_exponents_blk_ch(encoded_exp[blk][ch],
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exp[blk][ch], s->nb_coefs[ch],
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exp_strategy[blk][ch]);
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/* copy encoded exponents for reuse case */
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for (blk2 = blk+1; blk2 < blk1; blk2++) {
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memcpy(encoded_exp[blk2][ch], encoded_exp[blk][ch],
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s->nb_coefs[ch] * sizeof(uint8_t));
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}
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blk = blk1;
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}
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}
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return frame_bits;
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}
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/**
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* Calculate final exponents from the supplied MDCT coefficients and exponent shift.
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* Extract exponents from MDCT coefficients, calculate exponent strategies,
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* and encode final exponents.
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* @return bits needed to encode the exponents
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*/
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static int process_exponents(AC3EncodeContext *s,
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int32_t mdct_coef[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS],
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int8_t exp_shift[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS],
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uint8_t exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS],
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uint8_t exp_strategy[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS],
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uint8_t encoded_exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS])
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{
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extract_exponents(s, mdct_coef, exp_shift, exp);
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compute_exp_strategy(s, exp_strategy, exp);
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return encode_exponents(s, exp, exp_strategy, encoded_exp);
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}
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/**
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* Calculate the number of bits needed to encode a set of mantissas.
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*/
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@ -1174,8 +1286,7 @@ static int ac3_encode_frame(AVCodecContext *avctx,
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{
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AC3EncodeContext *s = avctx->priv_data;
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const int16_t *samples = data;
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int v;
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int blk, blk1, blk2, ch, i;
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int blk;
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int16_t planar_samples[AC3_MAX_CHANNELS][AC3_BLOCK_SIZE+AC3_FRAME_SIZE];
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int32_t mdct_coef[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS];
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uint8_t exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS];
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@ -1189,56 +1300,7 @@ static int ac3_encode_frame(AVCodecContext *avctx,
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apply_mdct(s, planar_samples, exp_shift, mdct_coef);
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/* extract exponents */
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for (ch = 0; ch < s->channels; ch++) {
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for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
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/* compute "exponents". We take into account the normalization there */
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for (i = 0; i < AC3_MAX_COEFS; i++) {
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int e;
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v = abs(mdct_coef[blk][ch][i]);
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if (v == 0)
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e = 24;
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else {
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e = 23 - av_log2(v) + exp_shift[blk][ch];
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if (e >= 24) {
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e = 24;
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mdct_coef[blk][ch][i] = 0;
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}
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}
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exp[blk][ch][i] = e;
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}
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}
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}
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/* compute exponent strategies */
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for (ch = 0; ch < s->channels; ch++) {
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compute_exp_strategy_ch(exp_strategy, exp, ch, ch == s->lfe_channel);
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}
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/* encode exponents */
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frame_bits = 0;
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for (ch = 0; ch < s->channels; ch++) {
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/* compute the exponents as the decoder will see them. The
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EXP_REUSE case must be handled carefully : we select the
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min of the exponents */
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blk = 0;
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while (blk < AC3_MAX_BLOCKS) {
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blk1 = blk + 1;
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while (blk1 < AC3_MAX_BLOCKS && exp_strategy[blk1][ch] == EXP_REUSE) {
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exponent_min(exp[blk][ch], exp[blk1][ch], s->nb_coefs[ch]);
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blk1++;
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}
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frame_bits += encode_exponents_blk_ch(encoded_exp[blk][ch],
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exp[blk][ch], s->nb_coefs[ch],
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exp_strategy[blk][ch]);
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/* copy encoded exponents for reuse case */
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for (blk2 = blk+1; blk2 < blk1; blk2++) {
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memcpy(encoded_exp[blk2][ch], encoded_exp[blk][ch],
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s->nb_coefs[ch] * sizeof(uint8_t));
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}
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blk = blk1;
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}
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}
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frame_bits = process_exponents(s, mdct_coef, exp_shift, exp, exp_strategy, encoded_exp);
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/* adjust for fractional frame sizes */
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while (s->bits_written >= s->bit_rate && s->samples_written >= s->sample_rate) {
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