[FFmpeg-devel] [PATCH] extract ff_celp_lspf2lpc to share with AMR SoC

[Kenan Gillet]

Hi all,

while working on the AMR SoC code, I stumble on some code
that could shared with the QCELP decoder.

The patch split  ff_qcelp_lspf2lpc into a more general sub-function
ff_celp_lspf2lpc which then can be shared with the AMR-NB SoC
code.

If approved, I will provide patches to move the specific QCELP
code into qcelpdec.c and qcelpdata.h.

thanks

Kenan
-------------- next part --------------
Index: libavcodec/qcelp_lsp.c
===================================================================
--- libavcodec/qcelp_lsp.c	(revision 17461)
+++ libavcodec/qcelp_lsp.c	(working copy)
@@ -48,16 +48,16 @@
  *
  * TIA/EIA/IS-733 2.4.3.3.5-1/2
  */
-static void lsp2polyf(const float *lspf, double *f, int lp_half_order)
+static void lsp2polyf(const double *lspf, double *f, int lp_half_order)
 {
     int i, j;
 
     f[0] = 1.0;
-    f[1] = -2 * cos(M_PI * lspf[0]);
+    f[1] = -2 * lspf[0];
     lspf -= 2;
     for(i=2; i<=lp_half_order; i++)
     {
-        double val = -2 * cos(M_PI * lspf[2*i]);
+        double val = -2 * lspf[2*i];
         f[i] = val * f[i-1] + 2*f[i-2];
         for(j=i-1; j>1; j--)
             f[j] += f[j-1] * val + f[j-2];
@@ -66,22 +66,15 @@
 }
 
 /**
- * Reconstructs LPC coefficients from the line spectral pair frequencies
- * and performs bandwidth expansion.
+ * Reconstructs LPC coefficients from the line spectral pair frequencies.
  *
  * @param lspf line spectral pair frequencies
  * @param lpc linear predictive coding coefficients
- *
- * @note: bandwith_expansion_coeff could be precalculated into a table
- *        but it seems to be slower on x86
- *
- * TIA/EIA/IS-733 2.4.3.3.5
  */
-void ff_qcelp_lspf2lpc(const float *lspf, float *lpc)
+void ff_celp_lspf2lpc(const double *lspf, float *lpc)
 {
     double pa[6], qa[6];
     int   i;
-    double bandwith_expansion_coeff = -QCELP_BANDWITH_EXPANSION_COEFF * 0.5;
 
     lsp2polyf(lspf,     pa, 5);
     lsp2polyf(lspf + 1, qa, 5);
@@ -91,10 +84,35 @@
         double paf = pa[i+1] + pa[i];
         double qaf = qa[i+1] - qa[i];
 
-        lpc[i  ] = paf + qaf;
-        lpc[9-i] = paf - qaf;
+        lpc[i  ] = 0.5 * (paf+qaf);
+        lpc[9-i] = 0.5 * (paf-qaf);
     }
+}
+
+/**
+ * Reconstructs LPC coefficients from the line spectral pair frequencies
+ * and performs bandwidth expansion.
+ *
+ * @param lspf line spectral pair frequencies
+ * @param lpc linear predictive coding coefficients
+ *
+ * @note: bandwith_expansion_coeff could be precalculated into a table
+ *        but it seems to be slower on x86
+ *
+ * TIA/EIA/IS-733 2.4.3.3.5
+ */
+void ff_qcelp_lspf2lpc(const float *lspf, float *lpc)
+{
+    double lsf[10];
+    double bandwith_expansion_coeff = -QCELP_BANDWITH_EXPANSION_COEFF;
+    int   i;
+
     for (i=0; i<10; i++)
+        lsf[i] = cos(M_PI * lspf[i]);
+
+    ff_celp_lspf2lpc(lsf, lpc);
+
+    for (i=0; i<10; i++)
     {
         lpc[i] *= bandwith_expansion_coeff;
         bandwith_expansion_coeff *= QCELP_BANDWITH_EXPANSION_COEFF;