Only do second sum if it can make a difference

1 files changed, 4 insertions, 2 deletions

diff --git a/lcs.c b/lcs.c
index b971c79..f3a6203 100644
--- a/lcs.c
+++ b/lcs.c
@@ -158,7 +158,7 @@ int lcs_32_rough(unsigned char *str1, unsigned char *str2) {
 #endif
 
 #ifdef USE_PRE_LCS
-//efine DO_SECOND_SUM
+#define DO_SECOND_SUM
 
 #ifdef DO_SECOND_SUM
 #include "arpa/inet.h"
@@ -188,7 +188,9 @@ int lcs_upper_bound(const uint32_t * const str1_int, const uint32_t * const str2
     // can be off up to two nibbles (e.g., "0110" and "1122")
     ret = first_sum * 2 + 2;
 #ifdef DO_SECOND_SUM
-    if (ret >= MSF) {
+    // We can only increase our accuracy by 1, so do second_sum only if we can
+    // turn a false-positive into a negative
+    if (ret == MSF) {
         uint32_t bo_str2_int[4];
         uint32_t shifted_str2_int[4];
         const unsigned char * const str2_r = (const unsigned char * const)shifted_str2_int;