1 files changed, 86 insertions, 0 deletions
diff --git a/third_party/libwebrtc/modules/audio_coding/codecs/ilbc/lsp_to_lsf.c b/third_party/libwebrtc/modules/audio_coding/codecs/ilbc/lsp_to_lsf.c
new file mode 100644
index 0000000000..227f4d45b4
--- /dev/null
+++ b/third_party/libwebrtc/modules/audio_coding/codecs/ilbc/lsp_to_lsf.c
@@ -0,0 +1,86 @@
+/*
+ *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+/******************************************************************
+
+ iLBC Speech Coder ANSI-C Source Code
+
+ WebRtcIlbcfix_Lsp2Lsf.c
+
+******************************************************************/
+
+#include "modules/audio_coding/codecs/ilbc/lsp_to_lsf.h"
+
+#include "modules/audio_coding/codecs/ilbc/constants.h"
+#include "modules/audio_coding/codecs/ilbc/defines.h"
+
+/*----------------------------------------------------------------*
+ *  conversion from LSP coefficients to LSF coefficients
+ *---------------------------------------------------------------*/
+
+void WebRtcIlbcfix_Lsp2Lsf(
+    int16_t *lsp, /* (i) lsp vector -1...+1 in Q15 */
+    int16_t *lsf, /* (o) Lsf vector 0...Pi in Q13
+                           (ordered, so that lsf[i]<lsf[i+1]) */
+    int16_t m  /* (i) Number of coefficients */
+                           )
+{
+  int16_t i, k;
+  int16_t diff; /* diff between table value and desired value (Q15) */
+  int16_t freq; /* lsf/(2*pi) (Q16) */
+  int16_t *lspPtr, *lsfPtr, *cosTblPtr;
+  int16_t tmp;
+
+  /* set the index to maximum index value in WebRtcIlbcfix_kCos */
+  k = 63;
+
+  /*
+     Start with the highest LSP and then work the way down
+     For each LSP the lsf is calculated by first order approximation
+     of the acos(x) function
+  */
+  lspPtr = &lsp[9];
+  lsfPtr = &lsf[9];
+  cosTblPtr=(int16_t*)&WebRtcIlbcfix_kCos[k];
+  for(i=m-1; i>=0; i--)
+  {
+    /*
+       locate value in the table, which is just above lsp[i],
+       basically an approximation to acos(x)
+    */
+    while( (((int32_t)(*cosTblPtr)-(*lspPtr)) < 0)&&(k>0) )
+    {
+      k-=1;
+      cosTblPtr--;
+    }
+
+    /* Calculate diff, which is used in the linear approximation of acos(x) */
+    diff = (*lspPtr)-(*cosTblPtr);
+
+    /*
+       The linear approximation of acos(lsp[i]) :
+       acos(lsp[i])= k*512 + (WebRtcIlbcfix_kAcosDerivative[ind]*offset >> 11)
+    */
+
+    /* tmp (linear offset) in Q16 */
+    tmp = (int16_t)((WebRtcIlbcfix_kAcosDerivative[k] * diff) >> 11);
+
+    /* freq in Q16 */
+    freq = (k << 9) + tmp;
+
+    /* lsf = freq*2*pi */
+    (*lsfPtr) = (int16_t)(((int32_t)freq*25736)>>15);
+
+    lsfPtr--;
+    lspPtr--;
+  }
+
+  return;
+}