namespace NSpeex
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{
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using System;
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internal class Lpc
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{
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public static void Autocorr(float[] x, float[] ac, int lag, int n)
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{
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while (lag-- > 0)
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{
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int index = lag;
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float num = 0f;
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while (index < n)
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{
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num += x[index] * x[index - lag];
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index++;
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}
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ac[lag] = num;
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}
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}
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public static float Wld(float[] lpc, float[] ac, float[] xref, int p)
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{
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int num;
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float num4 = ac[0];
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if (ac[0] == 0f)
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{
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for (num = 0; num < p; num++)
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{
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xref[num] = 0f;
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}
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return 0f;
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}
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for (num = 0; num < p; num++)
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{
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float num3 = -ac[num + 1];
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int index = 0;
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while (index < num)
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{
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num3 -= lpc[index] * ac[num - index];
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index++;
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}
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xref[num] = num3 /= num4;
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lpc[num] = num3;
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index = 0;
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while (index < (num / 2))
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{
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float num5 = lpc[index];
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lpc[index] += num3 * lpc[(num - 1) - index];
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lpc[(num - 1) - index] += num3 * num5;
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index++;
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}
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if ((num % 2) != 0)
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{
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lpc[index] += lpc[index] * num3;
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}
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float? nullable = 1f;
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num4 *= nullable.Value - (num3 * num3);
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}
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return num4;
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}
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}
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}
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