static void predictor_decompress_fir_adapt(int32_t *error_buffer, int32_t *buffer_out, int output_size, int readsamplesize, int16_t *predictor_coef_table, int predictor_coef_num, int predictor_quantitization) { int i; /* first sample always copies */ *buffer_out = *error_buffer; if (!predictor_coef_num) { if (output_size <= 1) return; memcpy(&buffer_out[1], &error_buffer[1], (output_size - 1) * sizeof(*buffer_out)); return; } if (predictor_coef_num == 31) { /* simple 1st-order prediction */ if (output_size <= 1) return; for (i = 1; i < output_size; i++) { buffer_out[i] = sign_extend(buffer_out[i - 1] + error_buffer[i], readsamplesize); } return; } /* read warm-up samples */ for (i = 0; i < predictor_coef_num; i++) { buffer_out[i + 1] = sign_extend(buffer_out[i] + error_buffer[i + 1], readsamplesize); } /* NOTE: 4 and 8 are very common cases that could be optimized. */ /* general case */ for (i = predictor_coef_num; i < output_size - 1; i++) { int j; int val = 0; int error_val = error_buffer[i + 1]; int error_sign; int d = buffer_out[i - predictor_coef_num]; for (j = 0; j < predictor_coef_num; j++) { val += (buffer_out[i - j] - d) * predictor_coef_table[j]; } val = (val + (1 << (predictor_quantitization - 1))) >> predictor_quantitization; val += d + error_val; buffer_out[i + 1] = sign_extend(val, readsamplesize); /* adapt LPC coefficients */ error_sign = sign_only(error_val); if (error_sign) { for (j = predictor_coef_num - 1; j >= 0 && error_val * error_sign > 0; j--) { int sign; val = d - buffer_out[i - j]; sign = sign_only(val) * error_sign; predictor_coef_table[j] -= sign; val *= sign; error_val -= ((val >> predictor_quantitization) * (predictor_coef_num - j)); } } } }