[FFmpeg-cvslog] lpc: add ff_lpc_calc_ref_coefs_f() function

[Rostislav Pehlivanov]

ffmpeg | branch: master | Rostislav Pehlivanov <atomnuker at gmail.com> | Tue Sep  1 06:34:50 2015 +0100| [0fc3a51353509df107a8da192d8377f0121f7ab9] | committer: Rostislav Pehlivanov

lpc: add ff_lpc_calc_ref_coefs_f() function

This commit adds a function to get the reflection coefficients on
floating point samples. It's functionally identical to
ff_lpc_calc_ref_coefs() except it works on float samples and will
return the global prediction gain. The Welch window implementation
which is more optimized works only on int32_t samples so a slower
generic expression was used.

Signed-off-by: Rostislav Pehlivanov <atomnuker at gmail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=0fc3a51353509df107a8da192d8377f0121f7ab9
---

 libavcodec/lpc.c |   20 ++++++++++++++++++++
 libavcodec/lpc.h |    2 ++
 2 files changed, 22 insertions(+)

diff --git a/libavcodec/lpc.c b/libavcodec/lpc.c
index 07fc292..315997c 100644
--- a/libavcodec/lpc.c
+++ b/libavcodec/lpc.c
@@ -167,6 +167,26 @@ int ff_lpc_calc_ref_coefs(LPCContext *s,
     return order;
 }
 
+double ff_lpc_calc_ref_coefs_f(LPCContext *s, const float *samples, int len,
+                               int order, double *ref)
+{
+    int i;
+    double signal = 0.0f, avg_err = 0.0f;
+    double autoc[MAX_LPC_ORDER+1] = {0}, error[MAX_LPC_ORDER] = {0};
+    const double c = (len - 1)/2.0f;
+
+    /* Welch window */
+    for (i = 0; i < len; i++)
+        s->windowed_samples[i] = 1.0f - ((samples[i]-c)/c)*((samples[i]-c)/c);
+
+    s->lpc_compute_autocorr(s->windowed_samples, len, order, autoc);
+    signal = autoc[0];
+    compute_ref_coefs(autoc, order, ref, error);
+    for (i = 0; i < order; i++)
+        avg_err = (avg_err + error[i])/2.0f;
+    return signal/avg_err;
+}
+
 /**
  * Calculate LPC coefficients for multiple orders
  *
diff --git a/libavcodec/lpc.h b/libavcodec/lpc.h
index 3aef623..7e0ee3e 100644
--- a/libavcodec/lpc.h
+++ b/libavcodec/lpc.h
@@ -100,6 +100,8 @@ int ff_lpc_calc_coefs(LPCContext *s,
 int ff_lpc_calc_ref_coefs(LPCContext *s,
                           const int32_t *samples, int order, double *ref);
 
+double ff_lpc_calc_ref_coefs_f(LPCContext *s, const float *samples, int len,
+                               int order, double *ref);
 
 /**
  * Initialize LPCContext.