1 files changed, 63 insertions, 0 deletions
diff --git a/third_party/libwebrtc/modules/audio_coding/codecs/ilbc/lsf_to_lsp.c b/third_party/libwebrtc/modules/audio_coding/codecs/ilbc/lsf_to_lsp.c
new file mode 100644
index 0000000000..ee8292f394
--- /dev/null
+++ b/third_party/libwebrtc/modules/audio_coding/codecs/ilbc/lsf_to_lsp.c
@@ -0,0 +1,63 @@
+/*
+ *  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_Lsf2Lsp.c
+
+******************************************************************/
+
+#include "modules/audio_coding/codecs/ilbc/lsf_to_lsp.h"
+
+#include "modules/audio_coding/codecs/ilbc/constants.h"
+#include "modules/audio_coding/codecs/ilbc/defines.h"
+
+/*----------------------------------------------------------------*
+ *  conversion from lsf to lsp coefficients
+ *---------------------------------------------------------------*/
+
+void WebRtcIlbcfix_Lsf2Lsp(
+    int16_t *lsf, /* (i) lsf in Q13 values between 0 and pi */
+    int16_t *lsp, /* (o) lsp in Q15 values between -1 and 1 */
+    int16_t m  /* (i) number of coefficients */
+                           ) {
+  int16_t i, k;
+  int16_t diff; /* difference, which is used for the
+                           linear approximation (Q8) */
+  int16_t freq; /* normalized frequency in Q15 (0..1) */
+  int32_t tmpW32;
+
+  for(i=0; i<m; i++)
+  {
+    freq = (int16_t)((lsf[i] * 20861) >> 15);
+    /* 20861: 1.0/(2.0*PI) in Q17 */
+    /*
+       Upper 8 bits give the index k and
+       Lower 8 bits give the difference, which needs
+       to be approximated linearly
+    */
+    k = freq >> 8;
+    diff = (freq&0x00ff);
+
+    /* Guard against getting outside table */
+
+    if (k>63) {
+      k = 63;
+    }
+
+    /* Calculate linear approximation */
+    tmpW32 = WebRtcIlbcfix_kCosDerivative[k] * diff;
+    lsp[i] = WebRtcIlbcfix_kCos[k] + (int16_t)(tmpW32 >> 12);
+  }
+
+  return;
+}