diff --git a/lib_dec/igf_dec_fx.c b/lib_dec/igf_dec_fx.c
index 206627d924110c06cda37ecd4a6277cde81385d3..59485575e837bf1554ab1fb8d3175968c2f7bc86 100644
--- a/lib_dec/igf_dec_fx.c
+++ b/lib_dec/igf_dec_fx.c
@@ -2905,6 +2905,7 @@ static void IGF_getWhiteSpectralData_ivas(
     Word16 tmp_e;
     Word16 out_e_arr[IGF_START_MX + MAX_IGF_SFB_LEN];
     Word16 max_out_e;
+    Word64 window_sum;
     assert( LT_16( stop, IGF_START_MX + MAX_IGF_SFB_LEN ) );
 
     /* inits */
@@ -2930,15 +2931,18 @@ static void IGF_getWhiteSpectralData_ivas(
     ak_e = add( tmp_e, sub( shl( sub( in_e, s_l ), 1 ), 15 ) ); // tmp_e + 2 * (in_e - s_l) - 15
     ak_e = sub( ak_e, 1 );
 
+    window_sum = 0;
+    move64();
+    FOR( j = start - level; j < start + level; j++ )
+    {
+        window_sum = W_mac_32_32( window_sum, in[j], in[j] );
+    }
+
     FOR( i = start; i < stop - level; i++ )
     {
-        Word64 temp = 0;
-        move64();
-        FOR( j = i - level; j < i + level + 1; j++ )
-        {
-            temp = W_mac_32_32( temp, in[j], in[j] );
-        }
-        ak = Mult_32_16( W_shl_sat_l( temp, shift ), quo ); // add( shl( level, 1 ), 1 ), &tmp_e ) );
+        window_sum = W_mac_32_32( window_sum, in[i + level], in[i + level] );           /* add the right one */
+        ak = Mult_32_16( W_shl_sat_l( window_sum, shift ), quo );                       // add( shl( level, 1 ), 1 ), &tmp_e ) );
+        window_sum = W_sub( window_sum, W_mult_32_32( in[i - level], in[i - level] ) ); /* subtract the left one */
 
 
         n = sub( ak_e, norm_l( ak ) );
@@ -2951,16 +2955,9 @@ static void IGF_getWhiteSpectralData_ivas(
 
     FOR( ; i < stop; i++ )
     {
-        Word64 temp = 0;
-        move64();
-
-        FOR( j = i - level; j < stop; j++ )
-        {
-            temp = W_mac_32_32( temp, in[j], in[j] );
-        }
-
-        ak = L_deposit_h( BASOP_Util_Divide3216_Scale( W_shl_sat_l( temp, shift ), sub( stop, sub( i, level ) ), &tmp_e ) );
-        ak_e = add( tmp_e, eff_e ); // tmp_e + 2 * (in_e - s_l) - 15
+        ak = L_deposit_h( BASOP_Util_Divide3216_Scale( W_shl_sat_l( window_sum, shift ), sub( stop, sub( i, level ) ), &tmp_e ) );
+        window_sum = W_sub( window_sum, W_mult_32_32( in[i - level], in[i - level] ) ); /* subtract the left one */
+        ak_e = add( tmp_e, eff_e );                                                     // tmp_e + 2 * (in_e - s_l) - 15
         n = sub( ak_e, add( norm_l( ak ), 1 ) );
         n = shr( n, 1 );