Do not hardcode filter order in ff_acelp_lspd2lpc()

Originally committed as revision 20485 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/lsp.c

@@ -155,20 +155,19 @@ static void lsp2polyf(const double *lsp, double *f, int lp_half_order)
     }
 }
 
-void ff_acelp_lspd2lpc(const double *lsp, float *lpc)
+void ff_acelp_lspd2lpc(const double *lsp, float *lpc, int lp_half_order)
 {
-    double pa[6], qa[6];
-    int   i;
+    double pa[lp_half_order+1], qa[lp_half_order+1];
+    float *lpc2 = lpc + (lp_half_order << 1) - 1;
 
-    lsp2polyf(lsp,     pa, 5);
-    lsp2polyf(lsp + 1, qa, 5);
+    lsp2polyf(lsp,     pa, lp_half_order);
+    lsp2polyf(lsp + 1, qa, lp_half_order);
 
-    for (i=4; i>=0; i--)
-    {
-        double paf = pa[i+1] + pa[i];
-        double qaf = qa[i+1] - qa[i];
+    while (lp_half_order--) {
+        double paf = pa[lp_half_order+1] + pa[lp_half_order];
+        double qaf = qa[lp_half_order+1] - qa[lp_half_order];
 
-        lpc[i  ] = 0.5*(paf+qaf);
-        lpc[9-i] = 0.5*(paf-qaf);
+        lpc [ lp_half_order] = 0.5*(paf+qaf);
+        lpc2[-lp_half_order] = 0.5*(paf-qaf);
     }
 }

libavcodec/lsp.h

@@ -86,8 +86,10 @@ void ff_acelp_lp_decode(int16_t* lp_1st, int16_t* lp_2nd, const int16_t* lsp_2nd
  * @param lsp line spectral pairs in cosine domain
  * @param lpc linear predictive coding coefficients
  *
+ * @note buffers should have a minimux size of 2*lp_half_order elements.
+ *
  * TIA/EIA/IS-733 2.4.3.3.5
  */
-void ff_acelp_lspd2lpc(const double *lsp, float *lpc);
+void ff_acelp_lspd2lpc(const double *lsp, float *lpc, int lp_half_order);
 
 #endif /* AVCODEC_LSP_H */

libavcodec/qcelpdec.c

@@ -578,7 +578,7 @@ static void lspf2lpc(const float *lspf, float *lpc)
     for (i=0; i<10; i++)
         lsp[i] = cos(M_PI * lspf[i]);
 
-    ff_acelp_lspd2lpc(lsp, lpc);
+    ff_acelp_lspd2lpc(lsp, lpc, 5);
 
     for (i=0; i<10; i++)
     {