static void lsp2lpc(int16_t *lpc) { int f1[LPC_ORDER / 2 + 1]; int f2[LPC_ORDER / 2 + 1]; int i, j; /* Calculate negative cosine */ for (j = 0; j < LPC_ORDER; j++) { int index = lpc[j] >> 7; int offset = lpc[j] & 0x7f; int temp1 = cos_tab[index] << 16; int temp2 = (cos_tab[index + 1] - cos_tab[index]) * ((offset << 8) + 0x80) << 1; lpc[j] = -(av_sat_dadd32(1 << 15, temp1 + temp2) >> 16); } /* * Compute sum and difference polynomial coefficients * (bitexact alternative to lsp2poly() in lsp.c) */ /* Initialize with values in Q28 */ f1[0] = 1 << 28; f1[1] = (lpc[0] << 14) + (lpc[2] << 14); f1[2] = lpc[0] * lpc[2] + (2 << 28); f2[0] = 1 << 28; f2[1] = (lpc[1] << 14) + (lpc[3] << 14); f2[2] = lpc[1] * lpc[3] + (2 << 28); /* * Calculate and scale the coefficients by 1/2 in * each iteration for a final scaling factor of Q25 */ for (i = 2; i < LPC_ORDER / 2; i++) { f1[i + 1] = f1[i - 1] + MULL2(f1[i], lpc[2 * i]); f2[i + 1] = f2[i - 1] + MULL2(f2[i], lpc[2 * i + 1]); for (j = i; j >= 2; j--) { f1[j] = MULL2(f1[j - 1], lpc[2 * i]) + (f1[j] >> 1) + (f1[j - 2] >> 1); f2[j] = MULL2(f2[j - 1], lpc[2 * i + 1]) + (f2[j] >> 1) + (f2[j - 2] >> 1); } f1[0] >>= 1; f2[0] >>= 1; f1[1] = ((lpc[2 * i] << 16 >> i) + f1[1]) >> 1; f2[1] = ((lpc[2 * i + 1] << 16 >> i) + f2[1]) >> 1; } /* Convert polynomial coefficients to LPC coefficients */ for (i = 0; i < LPC_ORDER / 2; i++) { int64_t ff1 = f1[i + 1] + f1[i]; int64_t ff2 = f2[i + 1] - f2[i]; lpc[i] = av_clipl_int32(((ff1 + ff2) << 3) + (1 << 15)) >> 16; lpc[LPC_ORDER - i - 1] = av_clipl_int32(((ff1 - ff2) << 3) + (1 << 15)) >> 16; } }