1 files changed, 57 insertions, 0 deletions
diff --git a/src/common_audio/signal_processing/lpc_to_refl_coef.c b/src/common_audio/signal_processing/lpc_to_refl_coef.c
new file mode 100644
index 0000000000..2cb83c2e1d
--- /dev/null
+++ b/src/common_audio/signal_processing/lpc_to_refl_coef.c
@@ -0,0 +1,57 @@
+/*
+ *  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.
+ */
+
+
+/*
+ * This file contains the function WebRtcSpl_LpcToReflCoef().
+ * The description header can be found in signal_processing_library.h
+ *
+ */
+
+#include "signal_processing_library.h"
+
+#define SPL_LPC_TO_REFL_COEF_MAX_AR_MODEL_ORDER 50
+
+void WebRtcSpl_LpcToReflCoef(WebRtc_Word16* a16, int use_order, WebRtc_Word16* k16)
+{
+    int m, k;
+    WebRtc_Word32 tmp32[SPL_LPC_TO_REFL_COEF_MAX_AR_MODEL_ORDER];
+    WebRtc_Word32 tmp_inv_denom32;
+    WebRtc_Word16 tmp_inv_denom16;
+
+    k16[use_order - 1] = WEBRTC_SPL_LSHIFT_W16(a16[use_order], 3); //Q12<<3 => Q15
+    for (m = use_order - 1; m > 0; m--)
+    {
+        // (1 - k^2) in Q30
+        tmp_inv_denom32 = ((WebRtc_Word32)1073741823) - WEBRTC_SPL_MUL_16_16(k16[m], k16[m]);
+        // (1 - k^2) in Q15
+        tmp_inv_denom16 = (WebRtc_Word16)WEBRTC_SPL_RSHIFT_W32(tmp_inv_denom32, 15);
+
+        for (k = 1; k <= m; k++)
+        {
+            // tmp[k] = (a[k] - RC[m] * a[m-k+1]) / (1.0 - RC[m]*RC[m]);
+
+            // [Q12<<16 - (Q15*Q12)<<1] = [Q28 - Q28] = Q28
+            tmp32[k] = WEBRTC_SPL_LSHIFT_W32((WebRtc_Word32)a16[k], 16)
+                    - WEBRTC_SPL_LSHIFT_W32(WEBRTC_SPL_MUL_16_16(k16[m], a16[m-k+1]), 1);
+
+            tmp32[k] = WebRtcSpl_DivW32W16(tmp32[k], tmp_inv_denom16); //Q28/Q15 = Q13
+        }
+
+        for (k = 1; k < m; k++)
+        {
+            a16[k] = (WebRtc_Word16)WEBRTC_SPL_RSHIFT_W32(tmp32[k], 1); //Q13>>1 => Q12
+        }
+
+        tmp32[m] = WEBRTC_SPL_SAT(8191, tmp32[m], -8191);
+        k16[m - 1] = (WebRtc_Word16)WEBRTC_SPL_LSHIFT_W32(tmp32[m], 2); //Q13<<2 => Q15
+    }
+    return;
+}