Split off celp_filters.[ch] from acelp_filters.[ch] for the QCELP decoder.

patch by Kenan Gillet, kenan.gillet gmail com

Originally committed as revision 15680 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/celp_filters.c

@@ -0,0 +1,86 @@
+/*
+ * various filters for ACELP-based codecs
+ *
+ * Copyright (c) 2008 Vladimir Voroshilov
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <inttypes.h>
+
+#include "avcodec.h"
+#include "celp_filters.h"
+
+void ff_celp_convolve_circ(
+        int16_t* fc_out,
+        const int16_t* fc_in,
+        const int16_t* filter,
+        int len)
+{
+    int i, k;
+
+    memset(fc_out, 0, len * sizeof(int16_t));
+
+    /* Since there are few pulses over an entire subframe (i.e. almost
+       all fc_in[i] are zero) it is faster to loop over fc_in first. */
+    for(i=0; i<len; i++)
+    {
+        if(fc_in[i])
+        {
+            for(k=0; k<i; k++)
+                fc_out[k] += (fc_in[i] * filter[len + k - i]) >> 15;
+
+            for(k=i; k<len; k++)
+                fc_out[k] += (fc_in[i] * filter[      k - i]) >> 15;
+        }
+    }
+}
+
+int ff_celp_lp_synthesis_filter(
+        int16_t *out,
+        const int16_t* filter_coeffs,
+        const int16_t* in,
+        int buffer_length,
+        int filter_length,
+        int stop_on_overflow,
+        int rounder)
+{
+    int i,n;
+
+    // These two lines are to avoid a -1 subtraction in the main loop
+    filter_length++;
+    filter_coeffs--;
+
+    for(n=0; n<buffer_length; n++)
+    {
+        int sum = rounder;
+        for(i=1; i<filter_length; i++)
+            sum -= filter_coeffs[i] * out[n-i];
+
+        sum = (sum >> 12) + in[n];
+
+        if(sum + 0x8000 > 0xFFFFU)
+        {
+            if(stop_on_overflow)
+                return 1;
+            sum = (sum >> 31) ^ 32767;
+        }
+        out[n] = sum;
+    }
+
+    return 0;
+}