Revision 7e0a284b libavcodec/ac3enc_fixed.c
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/** |
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* Shift each value in an array by a specified amount. |
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* @param src input array |
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* @param n number of values in the array |
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* @param shift shift amount (negative=right, positive=left) |
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*/ |
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static void shift_int32(int32_t *src, int n, int shift) |
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{
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int i; |
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if (shift > 0) {
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for (i = 0; i < n; i++) |
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src[i] <<= shift; |
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} else if (shift < 0) {
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shift = -shift; |
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for (i = 0; i < n; i++) |
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src[i] >>= shift; |
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} |
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} |
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/** |
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* Normalize the input samples to use the maximum available precision. |
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* This assumes signed 16-bit input samples. Exponents are reduced by 9 to |
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* match the 24-bit internal precision for MDCT coefficients. |
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* This assumes signed 16-bit input samples. |
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* |
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* @return exponent shift
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* @return coefficient shift
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*/ |
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static int normalize_samples(AC3EncodeContext *s) |
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{
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int v = 14 - log2_tab(s, s->windowed_samples, AC3_WINDOW_SIZE); |
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lshift_tab(s->windowed_samples, AC3_WINDOW_SIZE, v); |
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return v - 9;
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return 9 - v;
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} |
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/** |
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* Scale MDCT coefficients from float to fixed-point.
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* Scale MDCT coefficients to 24-bit fixed-point.
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*/ |
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static void scale_coefficients(AC3EncodeContext *s) |
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{
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/* scaling/conversion is obviously not needed for the fixed-point encoder |
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since the coefficients are already fixed-point. */ |
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return; |
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int blk, ch; |
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for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
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AC3Block *block = &s->blocks[blk]; |
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for (ch = 0; ch < s->channels; ch++) {
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shift_int32(block->mdct_coef[ch], AC3_MAX_COEFS, |
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block->coeff_shift[ch]); |
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} |
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} |
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} |
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