[xiph-commits] r11359 - trunk/speex/libspeex

[jm at svn.xiph.org]

Author: jm
Date: 2006-05-07 08:34:14 -0700 (Sun, 07 May 2006)
New Revision: 11359

Modified:
   trunk/speex/libspeex/fixed_generic.h
   trunk/speex/libspeex/lpc.c
Log:
Slight accuracy improvement in Levinson-Durbin algo for fixed-point.


Modified: trunk/speex/libspeex/fixed_generic.h
===================================================================
--- trunk/speex/libspeex/fixed_generic.h	2006-05-07 12:41:03 UTC (rev 11358)
+++ trunk/speex/libspeex/fixed_generic.h	2006-05-07 15:34:14 UTC (rev 11359)
@@ -84,6 +84,7 @@
 
 #define MAC16_16_Q11(c,a,b)     (ADD32((c),SHR(MULT16_16((a),(b)),11)))
 #define MAC16_16_Q13(c,a,b)     (ADD32((c),SHR(MULT16_16((a),(b)),13)))
+#define MAC16_16_P13(c,a,b)     (ADD32((c),SHR(ADD32(4096,MULT16_16((a),(b))),13)))
 
 #define MULT16_16_Q11_32(a,b) (SHR(MULT16_16((a),(b)),11))
 #define MULT16_16_Q13(a,b) (SHR(MULT16_16((a),(b)),13))

Modified: trunk/speex/libspeex/lpc.c
===================================================================
--- trunk/speex/libspeex/lpc.c	2006-05-07 12:41:03 UTC (rev 11358)
+++ trunk/speex/libspeex/lpc.c	2006-05-07 15:34:14 UTC (rev 11359)
@@ -94,7 +94,7 @@
       for (j = 0; j < i; j++) 
          rr = SUB32(rr,MULT16_16(lpc[j],ac[i - j]));
 #ifdef FIXED_POINT
-      r = DIV32_16(rr,ADD16(error,16));
+      r = DIV32_16(rr+PSHR32(error,1),ADD16(error,4));
 #else
       r = rr/(error+.003*ac[0]);
 #endif
@@ -103,11 +103,11 @@
       for (j = 0; j < i>>1; j++) 
       {
          spx_word16_t tmp  = lpc[j];
-         lpc[j]     = MAC16_16_Q13(lpc[j],r,lpc[i-1-j]);
-         lpc[i-1-j] = MAC16_16_Q13(lpc[i-1-j],r,tmp);
+         lpc[j]     = MAC16_16_P13(lpc[j],r,lpc[i-1-j]);
+         lpc[i-1-j] = MAC16_16_P13(lpc[i-1-j],r,tmp);
       }
       if (i & 1) 
-         lpc[j] = MAC16_16_Q13(lpc[j],lpc[j],r);
+         lpc[j] = MAC16_16_P13(lpc[j],lpc[j],r);
 
       error = SUB16(error,MULT16_16_Q13(r,MULT16_16_Q13(error,r)));
    }