--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/intercom/ilbc/filter.c	Fri Jun 25 09:57:52 2010 +0200
@@ -0,0 +1,166 @@
+
+   /******************************************************************
+
+       iLBC Speech Coder ANSI-C Source Code
+
+       filter.c
+
+       Copyright (C) The Internet Society (2004).
+       All Rights Reserved.
+
+   ******************************************************************/
+
+#include "iLBC_define.h"
+
+   /*----------------------------------------------------------------*
+    *  all-pole filter
+    *---------------------------------------------------------------*/
+
+void AllPoleFilter(float *InOut,        /* (i/o) on entrance InOut[-orderCoef] to
+                                           InOut[-1] contain the state of the
+                                           filter (delayed samples). InOut[0] to
+                                           InOut[lengthInOut-1] contain the filter
+                                           input, on en exit InOut[-orderCoef] to
+                                           InOut[-1] is unchanged and InOut[0] to
+                                           InOut[lengthInOut-1] contain filtered
+                                           samples */
+  float *Coef,                  /* (i) filter coefficients, Coef[0] is assumed
+                                   to be 1.0 */
+  int lengthInOut,              /* (i) number of input/output samples */
+  int orderCoef                 /* (i) number of filter coefficients */
+  )
+{
+  int n, k;
+
+  for (n = 0; n < lengthInOut; n++) {
+    for (k = 1; k <= orderCoef; k++) {
+      *InOut -= Coef[k] * InOut[-k];
+
+
+
+
+
+    }
+    InOut++;
+  }
+}
+
+   /*----------------------------------------------------------------*
+    *  all-zero filter
+    *---------------------------------------------------------------*/
+
+void AllZeroFilter(float *In,   /* (i) In[0] to In[lengthInOut-1] contain
+                                   filter input samples */
+  float *Coef,                  /* (i) filter coefficients (Coef[0] is assumed
+                                   to be 1.0) */
+  int lengthInOut,              /* (i) number of input/output samples */
+  int orderCoef,                /* (i) number of filter coefficients */
+  float *Out                    /* (i/o) on entrance Out[-orderCoef] to Out[-1]
+                                   contain the filter state, on exit Out[0]
+                                   to Out[lengthInOut-1] contain filtered
+                                   samples */
+  )
+{
+  int n, k;
+
+  for (n = 0; n < lengthInOut; n++) {
+    *Out = Coef[0] * In[0];
+    for (k = 1; k <= orderCoef; k++) {
+      *Out += Coef[k] * In[-k];
+    }
+    Out++;
+    In++;
+  }
+}
+
+   /*----------------------------------------------------------------*
+    *  pole-zero filter
+    *---------------------------------------------------------------*/
+
+void ZeroPoleFilter(float *In,  /* (i) In[0] to In[lengthInOut-1] contain
+                                   filter input samples In[-orderCoef] to
+                                   In[-1] contain state of all-zero
+                                   section */
+  float *ZeroCoef,              /* (i) filter coefficients for all-zero
+                                   section (ZeroCoef[0] is assumed to
+                                   be 1.0) */
+  float *PoleCoef,              /* (i) filter coefficients for all-pole section
+                                   (ZeroCoef[0] is assumed to be 1.0) */
+  int lengthInOut,              /* (i) number of input/output samples */
+  int orderCoef,                /* (i) number of filter coefficients */
+  float *Out                    /* (i/o) on entrance Out[-orderCoef] to Out[-1]
+                                   contain state of all-pole section. On
+                                   exit Out[0] to Out[lengthInOut-1]
+                                   contain filtered samples */
+  )
+{
+  AllZeroFilter(In, ZeroCoef, lengthInOut, orderCoef, Out);
+  AllPoleFilter(Out, PoleCoef, lengthInOut, orderCoef);
+}
+
+   /*----------------------------------------------------------------*
+    * downsample (LP filter and decimation)
+    *---------------------------------------------------------------*/
+
+void DownSample(float *In,      /* (i) input samples */
+  float *Coef,                  /* (i) filter coefficients */
+  int lengthIn,                 /* (i) number of input samples */
+  float *state,                 /* (i) filter state */
+  float *Out                    /* (o) downsampled output */
+  )
+{
+  float o;
+  float *Out_ptr = Out;
+  float *Coef_ptr, *In_ptr;
+  float *state_ptr;
+  int i, j, stop;
+
+  /* LP filter and decimate at the same time */
+
+  for (i = DELAY_DS; i < lengthIn; i += FACTOR_DS) {
+    Coef_ptr = &Coef[0];
+    In_ptr = &In[i];
+    state_ptr = &state[FILTERORDER_DS - 2];
+
+    o = (float) 0.0;
+
+    stop = (i < FILTERORDER_DS) ? i + 1 : FILTERORDER_DS;
+
+    for (j = 0; j < stop; j++) {
+      o += *Coef_ptr++ * (*In_ptr--);
+    }
+    for (j = i + 1; j < FILTERORDER_DS; j++) {
+      o += *Coef_ptr++ * (*state_ptr--);
+    }
+
+
+
+
+
+
+    *Out_ptr++ = o;
+  }
+
+  /* Get the last part (use zeros as input for the future) */
+
+  for (i = (lengthIn + FACTOR_DS); i < (lengthIn + DELAY_DS);
+    i += FACTOR_DS) {
+
+    o = (float) 0.0;
+
+    if (i < lengthIn) {
+      Coef_ptr = &Coef[0];
+      In_ptr = &In[i];
+      for (j = 0; j < FILTERORDER_DS; j++) {
+        o += *Coef_ptr++ * (*Out_ptr--);
+      }
+    } else {
+      Coef_ptr = &Coef[i - lengthIn];
+      In_ptr = &In[lengthIn - 1];
+      for (j = 0; j < FILTERORDER_DS - (i - lengthIn); j++) {
+        o += *Coef_ptr++ * (*In_ptr--);
+      }
+    }
+    *Out_ptr++ = o;
+  }
+}