From c50da3ad6c5ee316bafd38170172dcc6c3163764 Mon Sep 17 00:00:00 2001
From: Ramiro Polla <ramiro.polla@gmail.com>
Date: Sat, 16 Aug 2008 17:18:20 +0000
Subject: flacenc, lpc: Move LPC code from flacenc.c to new lpc.[ch] files.

Originally committed as revision 14790 to svn://svn.ffmpeg.org/ffmpeg/trunk
---
 libavcodec/lpc.c | 204 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 204 insertions(+)
 create mode 100644 libavcodec/lpc.c

(limited to 'libavcodec/lpc.c')

diff --git a/libavcodec/lpc.c b/libavcodec/lpc.c
new file mode 100644
index 0000000000..2c34233ead
--- /dev/null
+++ b/libavcodec/lpc.c
@@ -0,0 +1,204 @@
+/**
+ * LPC utility code
+ * Copyright (c) 2006  Justin Ruggles <jruggle@earthlink.net>
+ *
+ * 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 "libavutil/lls.h"
+#include "dsputil.h"
+#include "lpc.h"
+
+
+/**
+ * Levinson-Durbin recursion.
+ * Produces LPC coefficients from autocorrelation data.
+ */
+static void compute_lpc_coefs(const double *autoc, int max_order,
+                              double lpc[][MAX_LPC_ORDER], double *ref)
+{
+   int i, j, i2;
+   double r, err, tmp;
+   double lpc_tmp[MAX_LPC_ORDER];
+
+   for(i=0; i<max_order; i++) lpc_tmp[i] = 0;
+   err = autoc[0];
+
+   for(i=0; i<max_order; i++) {
+      r = -autoc[i+1];
+      for(j=0; j<i; j++) {
+          r -= lpc_tmp[j] * autoc[i-j];
+      }
+      r /= err;
+      ref[i] = fabs(r);
+
+      err *= 1.0 - (r * r);
+
+      i2 = (i >> 1);
+      lpc_tmp[i] = r;
+      for(j=0; j<i2; j++) {
+         tmp = lpc_tmp[j];
+         lpc_tmp[j] += r * lpc_tmp[i-1-j];
+         lpc_tmp[i-1-j] += r * tmp;
+      }
+      if(i & 1) {
+          lpc_tmp[j] += lpc_tmp[j] * r;
+      }
+
+      for(j=0; j<=i; j++) {
+          lpc[i][j] = -lpc_tmp[j];
+      }
+   }
+}
+
+/**
+ * Quantize LPC coefficients
+ */
+static void quantize_lpc_coefs(double *lpc_in, int order, int precision,
+                               int32_t *lpc_out, int *shift, int max_shift, int zero_shift)
+{
+    int i;
+    double cmax, error;
+    int32_t qmax;
+    int sh;
+
+    /* define maximum levels */
+    qmax = (1 << (precision - 1)) - 1;
+
+    /* find maximum coefficient value */
+    cmax = 0.0;
+    for(i=0; i<order; i++) {
+        cmax= FFMAX(cmax, fabs(lpc_in[i]));
+    }
+
+    /* if maximum value quantizes to zero, return all zeros */
+    if(cmax * (1 << max_shift) < 1.0) {
+        *shift = zero_shift;
+        memset(lpc_out, 0, sizeof(int32_t) * order);
+        return;
+    }
+
+    /* calculate level shift which scales max coeff to available bits */
+    sh = max_shift;
+    while((cmax * (1 << sh) > qmax) && (sh > 0)) {
+        sh--;
+    }
+
+    /* since negative shift values are unsupported in decoder, scale down
+       coefficients instead */
+    if(sh == 0 && cmax > qmax) {
+        double scale = ((double)qmax) / cmax;
+        for(i=0; i<order; i++) {
+            lpc_in[i] *= scale;
+        }
+    }
+
+    /* output quantized coefficients and level shift */
+    error=0;
+    for(i=0; i<order; i++) {
+        error += lpc_in[i] * (1 << sh);
+        lpc_out[i] = av_clip(lrintf(error), -qmax, qmax);
+        error -= lpc_out[i];
+    }
+    *shift = sh;
+}
+
+static int estimate_best_order(double *ref, int max_order)
+{
+    int i, est;
+
+    est = 1;
+    for(i=max_order-1; i>=0; i--) {
+        if(ref[i] > 0.10) {
+            est = i+1;
+            break;
+        }
+    }
+    return est;
+}
+
+/**
+ * Calculate LPC coefficients for multiple orders
+ */
+int ff_lpc_calc_coefs(DSPContext *s,
+                          const int32_t *samples, int blocksize, int max_order,
+                          int precision, int32_t coefs[][MAX_LPC_ORDER],
+                          int *shift, int use_lpc, int omethod, int max_shift, int zero_shift)
+{
+    double autoc[MAX_LPC_ORDER+1];
+    double ref[MAX_LPC_ORDER];
+    double lpc[MAX_LPC_ORDER][MAX_LPC_ORDER];
+    int i, j, pass;
+    int opt_order;
+
+    assert(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER);
+
+    if(use_lpc == 1){
+        s->flac_compute_autocorr(samples, blocksize, max_order, autoc);
+
+        compute_lpc_coefs(autoc, max_order, lpc, ref);
+    }else{
+        LLSModel m[2];
+        double var[MAX_LPC_ORDER+1], weight;
+
+        for(pass=0; pass<use_lpc-1; pass++){
+            av_init_lls(&m[pass&1], max_order);
+
+            weight=0;
+            for(i=max_order; i<blocksize; i++){
+                for(j=0; j<=max_order; j++)
+                    var[j]= samples[i-j];
+
+                if(pass){
+                    double eval, inv, rinv;
+                    eval= av_evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);
+                    eval= (512>>pass) + fabs(eval - var[0]);
+                    inv = 1/eval;
+                    rinv = sqrt(inv);
+                    for(j=0; j<=max_order; j++)
+                        var[j] *= rinv;
+                    weight += inv;
+                }else
+                    weight++;
+
+                av_update_lls(&m[pass&1], var, 1.0);
+            }
+            av_solve_lls(&m[pass&1], 0.001, 0);
+        }
+
+        for(i=0; i<max_order; i++){
+            for(j=0; j<max_order; j++)
+                lpc[i][j]= m[(pass-1)&1].coeff[i][j];
+            ref[i]= sqrt(m[(pass-1)&1].variance[i] / weight) * (blocksize - max_order) / 4000;
+        }
+        for(i=max_order-1; i>0; i--)
+            ref[i] = ref[i-1] - ref[i];
+    }
+    opt_order = max_order;
+
+    if(omethod == ORDER_METHOD_EST) {
+        opt_order = estimate_best_order(ref, max_order);
+        i = opt_order-1;
+        quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
+    } else {
+        for(i=0; i<max_order; i++) {
+            quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
+        }
+    }
+
+    return opt_order;
+}
-- 
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