From fde82ca7e4e72226da99d86a9fa9689136461d14 Mon Sep 17 00:00:00 2001
From: Justin Ruggles <justin.ruggles@gmail.com>
Date: Sat, 17 Oct 2009 21:00:39 +0000
Subject: Move autocorrelation function from flacenc.c to lpc.c. Also rename
 the corresponding dsputil functions and remove their dependency on the FLAC
 encoder. Fixes Issue1486.

Originally committed as revision 20266 to svn://svn.ffmpeg.org/ffmpeg/trunk
---
 libavcodec/lpc.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 63 insertions(+), 1 deletion(-)

(limited to 'libavcodec/lpc.c')

diff --git a/libavcodec/lpc.c b/libavcodec/lpc.c
index 896db51759..49e41d8c34 100644
--- a/libavcodec/lpc.c
+++ b/libavcodec/lpc.c
@@ -26,6 +26,68 @@
 #include "lpc.h"
 
 
+/**
+ * Apply Welch window function to audio block
+ */
+static void apply_welch_window(const int32_t *data, int len, double *w_data)
+{
+    int i, n2;
+    double w;
+    double c;
+
+    assert(!(len&1)); //the optimization in r11881 does not support odd len
+                      //if someone wants odd len extend the change in r11881
+
+    n2 = (len >> 1);
+    c = 2.0 / (len - 1.0);
+
+    w_data+=n2;
+      data+=n2;
+    for(i=0; i<n2; i++) {
+        w = c - n2 + i;
+        w = 1.0 - (w * w);
+        w_data[-i-1] = data[-i-1] * w;
+        w_data[+i  ] = data[+i  ] * w;
+    }
+}
+
+/**
+ * Calculates autocorrelation data from audio samples
+ * A Welch window function is applied before calculation.
+ */
+void ff_lpc_compute_autocorr(const int32_t *data, int len, int lag,
+                             double *autoc)
+{
+    int i, j;
+    double tmp[len + lag + 1];
+    double *data1= tmp + lag;
+
+    apply_welch_window(data, len, data1);
+
+    for(j=0; j<lag; j++)
+        data1[j-lag]= 0.0;
+    data1[len] = 0.0;
+
+    for(j=0; j<lag; j+=2){
+        double sum0 = 1.0, sum1 = 1.0;
+        for(i=j; i<len; i++){
+            sum0 += data1[i] * data1[i-j];
+            sum1 += data1[i] * data1[i-j-1];
+        }
+        autoc[j  ] = sum0;
+        autoc[j+1] = sum1;
+    }
+
+    if(j==lag){
+        double sum = 1.0;
+        for(i=j-1; i<len; i+=2){
+            sum += data1[i  ] * data1[i-j  ]
+                 + data1[i+1] * data1[i-j+1];
+        }
+        autoc[j] = sum;
+    }
+}
+
 /**
  * Quantize LPC coefficients
  */
@@ -115,7 +177,7 @@ int ff_lpc_calc_coefs(DSPContext *s,
     assert(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER && use_lpc > 0);
 
     if(use_lpc == 1){
-        s->flac_compute_autocorr(samples, blocksize, max_order, autoc);
+        s->lpc_compute_autocorr(samples, blocksize, max_order, autoc);
 
         compute_lpc_coefs(autoc, max_order, &lpc[0][0], MAX_LPC_ORDER, 0, 1);
 
-- 
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