Merge "Prevent overflow in usac filters"

3 files changed, 9 insertions, 10 deletions

diff --git a/libAACdec/src/usacdec_acelp.cpp b/libAACdec/src/usacdec_acelp.cpp
index af1f488..9fecebf 100644
--- a/libAACdec/src/usacdec_acelp.cpp
+++ b/libAACdec/src/usacdec_acelp.cpp
@@ -579,11 +579,11 @@ void Syn_filt(const FIXP_LPC a[], /* (i) : a[m] prediction coefficients Q12 */
     L_tmp = (FIXP_DBL)0;
 
     for (j = 0; j < M_LP_FILTER_ORDER; j++) {
-      L_tmp -= fMultDiv2(a[j], y[i - (j + 1)]);
+      L_tmp -= fMultDiv2(a[j], y[i - (j + 1)]) >> (LP_FILTER_SCALE - 1);
     }
 
-    L_tmp = scaleValue(L_tmp, a_exp + 1);
-    y[i] = L_tmp + x[i];
+    L_tmp = scaleValue(L_tmp, a_exp + LP_FILTER_SCALE);
+    y[i] = fAddSaturate(L_tmp, x[i]);
   }
 
   return;
@@ -631,10 +631,10 @@ void E_UTIL_residu(const FIXP_LPC *a, const INT a_exp, FIXP_DBL *x, FIXP_DBL *y,
     s = (FIXP_DBL)0;
 
     for (j = 0; j < M_LP_FILTER_ORDER; j++) {
-      s += fMultDiv2(a[j], x[i - j - 1]);
+      s += fMultDiv2(a[j], x[i - j - 1]) >> (LP_FILTER_SCALE - 1);
     }
 
-    s = scaleValue(s, a_exp + 1);
+    s = scaleValue(s, a_exp + LP_FILTER_SCALE);
     y[i] = fAddSaturate(s, x[i]);
   }
 
diff --git a/libAACdec/src/usacdec_const.h b/libAACdec/src/usacdec_const.h
index c7dbae7..f68e808 100644
--- a/libAACdec/src/usacdec_const.h
+++ b/libAACdec/src/usacdec_const.h
@@ -115,6 +115,7 @@ amm-info@iis.fraunhofer.de
 
 /* definitions which are independent of coreCoderFrameLength */
 #define M_LP_FILTER_ORDER 16 /* LP filter order */
+#define LP_FILTER_SCALE 4    /* LP filter scale */
 
 #define PIT_MIN_12k8 34    /* Minimum pitch lag with resolution 1/4 */
 #define PIT_MAX_12k8 231   /* Maximum pitch lag for fs=12.8kHz */
diff --git a/libAACdec/src/usacdec_fac.cpp b/libAACdec/src/usacdec_fac.cpp
index 25d3119..c10a3fe 100644
--- a/libAACdec/src/usacdec_fac.cpp
+++ b/libAACdec/src/usacdec_fac.cpp
@@ -191,13 +191,11 @@ static void Syn_filt_zero(const FIXP_LPC a[], const INT a_exp, INT length,
     L_tmp = (FIXP_DBL)0;
 
     for (j = 0; j < fMin(i, M_LP_FILTER_ORDER); j++) {
-      L_tmp -= fMultDiv2(a[j], x[i - (j + 1)]);
+      L_tmp -= fMultDiv2(a[j], x[i - (j + 1)]) >> (LP_FILTER_SCALE - 1);
     }
 
-    L_tmp = scaleValue(L_tmp, a_exp + 1);
-
-    x[i] = scaleValueSaturate((x[i] >> 1) + (L_tmp >> 1),
-                              1); /* Avoid overflow issues and saturate. */
+    L_tmp = scaleValue(L_tmp, a_exp + LP_FILTER_SCALE);
+    x[i] = fAddSaturate(x[i], L_tmp);
   }
 }