--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/intercom/ilbc/lsf.c	Fri Jun 25 09:57:52 2010 +0200
@@ -0,0 +1,269 @@
+
+   /******************************************************************
+
+       iLBC Speech Coder ANSI-C Source Code
+
+       lsf.c
+
+       Copyright (C) The Internet Society (2004).
+       All Rights Reserved.
+
+   ******************************************************************/
+
+#include <string.h>
+
+
+
+
+
+#include <math.h>
+
+#include "iLBC_define.h"
+
+   /*----------------------------------------------------------------*
+    *  conversion from lpc coefficients to lsf coefficients
+    *---------------------------------------------------------------*/
+
+void a2lsf(float *freq,         /* (o) lsf coefficients */
+  float *a                      /* (i) lpc coefficients */
+  )
+{
+  float steps[LSF_NUMBER_OF_STEPS] =
+    { (float) 0.00635, (float) 0.003175, (float) 0.0015875,
+    (float) 0.00079375
+  };
+  float step;
+  int step_idx;
+  int lsp_index;
+  float p[LPC_HALFORDER];
+  float q[LPC_HALFORDER];
+  float p_pre[LPC_HALFORDER];
+  float q_pre[LPC_HALFORDER];
+  float old_p, old_q, *old;
+  float *pq_coef;
+  float omega, old_omega;
+  int i;
+  float hlp, hlp1, hlp2, hlp3, hlp4, hlp5;
+
+  for (i = 0; i < LPC_HALFORDER; i++) {
+    p[i] = (float) -1.0 * (a[i + 1] + a[LPC_FILTERORDER - i]);
+    q[i] = a[LPC_FILTERORDER - i] - a[i + 1];
+  }
+
+  p_pre[0] = (float) -1.0 - p[0];
+  p_pre[1] = -p_pre[0] - p[1];
+  p_pre[2] = -p_pre[1] - p[2];
+  p_pre[3] = -p_pre[2] - p[3];
+  p_pre[4] = -p_pre[3] - p[4];
+  p_pre[4] = p_pre[4] / 2;
+
+  q_pre[0] = (float) 1.0 - q[0];
+  q_pre[1] = q_pre[0] - q[1];
+  q_pre[2] = q_pre[1] - q[2];
+  q_pre[3] = q_pre[2] - q[3];
+  q_pre[4] = q_pre[3] - q[4];
+  q_pre[4] = q_pre[4] / 2;
+
+  omega = 0.0;
+
+
+
+
+
+  old_omega = 0.0;
+
+  old_p = FLOAT_MAX;
+  old_q = FLOAT_MAX;
+
+  /* Here we loop through lsp_index to find all the
+     LPC_FILTERORDER roots for omega. */
+
+  for (lsp_index = 0; lsp_index < LPC_FILTERORDER; lsp_index++) {
+
+    /* Depending on lsp_index being even or odd, we
+       alternatively solve the roots for the two LSP equations. */
+
+
+    if ((lsp_index & 0x1) == 0) {
+      pq_coef = p_pre;
+      old = &old_p;
+    } else {
+      pq_coef = q_pre;
+      old = &old_q;
+    }
+
+    /* Start with low resolution grid */
+
+    for (step_idx = 0, step = steps[step_idx];
+      step_idx < LSF_NUMBER_OF_STEPS;) {
+
+      /*  cos(10piw) + pq(0)cos(8piw) + pq(1)cos(6piw) +
+         pq(2)cos(4piw) + pq(3)cod(2piw) + pq(4) */
+
+      hlp = (float) cos(omega * TWO_PI);
+      hlp1 = (float) 2.0 *hlp + pq_coef[0];
+      hlp2 = (float) 2.0 *hlp * hlp1 - (float) 1.0 + pq_coef[1];
+      hlp3 = (float) 2.0 *hlp * hlp2 - hlp1 + pq_coef[2];
+      hlp4 = (float) 2.0 *hlp * hlp3 - hlp2 + pq_coef[3];
+      hlp5 = hlp * hlp4 - hlp3 + pq_coef[4];
+
+
+      if (((hlp5 * (*old)) <= 0.0) || (omega >= 0.5)) {
+
+        if (step_idx == (LSF_NUMBER_OF_STEPS - 1)) {
+
+          if (fabs(hlp5) >= fabs(*old)) {
+            freq[lsp_index] = omega - step;
+          } else {
+            freq[lsp_index] = omega;
+          }
+
+
+
+
+
+
+
+          if ((*old) >= 0.0) {
+            *old = (float) -1.0 * FLOAT_MAX;
+          } else {
+            *old = FLOAT_MAX;
+          }
+
+          omega = old_omega;
+          step_idx = 0;
+
+          step_idx = LSF_NUMBER_OF_STEPS;
+        } else {
+
+          if (step_idx == 0) {
+            old_omega = omega;
+          }
+
+          step_idx++;
+          omega -= steps[step_idx];
+
+          /* Go back one grid step */
+
+          step = steps[step_idx];
+        }
+      } else {
+
+        /* increment omega until they are of different sign,
+           and we know there is at least one root between omega
+           and old_omega */
+        *old = hlp5;
+        omega += step;
+      }
+    }
+  }
+
+  for (i = 0; i < LPC_FILTERORDER; i++) {
+    freq[i] = freq[i] * TWO_PI;
+  }
+}
+
+   /*----------------------------------------------------------------*
+    *  conversion from lsf coefficients to lpc coefficients
+    *---------------------------------------------------------------*/
+
+void lsf2a(float *a_coef,       /* (o) lpc coefficients */
+  float *freq                   /* (i) lsf coefficients */
+  )
+{
+  int i, j;
+  float hlp;
+  float p[LPC_HALFORDER], q[LPC_HALFORDER];
+  float a[LPC_HALFORDER + 1], a1[LPC_HALFORDER], a2[LPC_HALFORDER];
+  float b[LPC_HALFORDER + 1], b1[LPC_HALFORDER], b2[LPC_HALFORDER];
+
+  for (i = 0; i < LPC_FILTERORDER; i++) {
+    freq[i] = freq[i] * PI2;
+  }
+
+  /* Check input for ill-conditioned cases.  This part is not
+     found in the TIA standard.  It involves the following 2 IF
+     blocks.  If "freq" is judged ill-conditioned, then we first
+     modify freq[0] and freq[LPC_HALFORDER-1] (normally
+     LPC_HALFORDER = 10 for LPC applications), then we adjust
+     the other "freq" values slightly */
+
+
+  if ((freq[0] <= 0.0) || (freq[LPC_FILTERORDER - 1] >= 0.5)) {
+
+
+    if (freq[0] <= 0.0) {
+      freq[0] = (float) 0.022;
+    }
+
+
+    if (freq[LPC_FILTERORDER - 1] >= 0.5) {
+      freq[LPC_FILTERORDER - 1] = (float) 0.499;
+    }
+
+    hlp = (freq[LPC_FILTERORDER - 1] - freq[0]) /
+      (float) (LPC_FILTERORDER - 1);
+
+    for (i = 1; i < LPC_FILTERORDER; i++) {
+      freq[i] = freq[i - 1] + hlp;
+    }
+  }
+
+  memset(a1, 0, LPC_HALFORDER * sizeof(float));
+  memset(a2, 0, LPC_HALFORDER * sizeof(float));
+  memset(b1, 0, LPC_HALFORDER * sizeof(float));
+  memset(b2, 0, LPC_HALFORDER * sizeof(float));
+  memset(a, 0, (LPC_HALFORDER + 1) * sizeof(float));
+  memset(b, 0, (LPC_HALFORDER + 1) * sizeof(float));
+
+
+
+
+
+
+  /* p[i] and q[i] compute cos(2*pi*omega_{2j}) and
+     cos(2*pi*omega_{2j-1} in eqs. 4.2.2.2-1 and 4.2.2.2-2.
+     Note that for this code p[i] specifies the coefficients
+     used in .Q_A(z) while q[i] specifies the coefficients used
+     in .P_A(z) */
+
+  for (i = 0; i < LPC_HALFORDER; i++) {
+    p[i] = (float) cos(TWO_PI * freq[2 * i]);
+    q[i] = (float) cos(TWO_PI * freq[2 * i + 1]);
+  }
+
+  a[0] = 0.25;
+  b[0] = 0.25;
+
+  for (i = 0; i < LPC_HALFORDER; i++) {
+    a[i + 1] = a[i] - 2 * p[i] * a1[i] + a2[i];
+    b[i + 1] = b[i] - 2 * q[i] * b1[i] + b2[i];
+    a2[i] = a1[i];
+    a1[i] = a[i];
+    b2[i] = b1[i];
+    b1[i] = b[i];
+  }
+
+  for (j = 0; j < LPC_FILTERORDER; j++) {
+
+    if (j == 0) {
+      a[0] = 0.25;
+      b[0] = -0.25;
+    } else {
+      a[0] = b[0] = 0.0;
+    }
+
+    for (i = 0; i < LPC_HALFORDER; i++) {
+      a[i + 1] = a[i] - 2 * p[i] * a1[i] + a2[i];
+      b[i + 1] = b[i] - 2 * q[i] * b1[i] + b2[i];
+      a2[i] = a1[i];
+      a1[i] = a[i];
+      b2[i] = b1[i];
+      b1[i] = b[i];
+    }
+
+    a_coef[j + 1] = 2 * (a[LPC_HALFORDER] + b[LPC_HALFORDER]);
+  }
+
+  a_coef[0] = 1.0;
+}