Auto-choose at runtime to do second sum in lcs_upper_bound

This has no impact for non-DO_SECOND_SUM, but puts DO_SECOND_SUM less than a
percent behind.

1 files changed, 27 insertions, 27 deletions

diff --git a/lcs.c b/lcs.c
index d296ea7..b971c79 100644
--- a/lcs.c
+++ b/lcs.c
@@ -170,22 +170,6 @@ int lcs_upper_bound(const uint32_t * const str1_int, const uint32_t * const str2
     const unsigned char * const str2 = (const unsigned char * const)str2_int;
     int first_sum;
     int ret;
-#ifdef DO_SECOND_SUM
-    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;
-    int second_sum;
-
-    bo_str2_int[0] = ntohl(str2_int[0]);
-    bo_str2_int[1] = ntohl(str2_int[1]);
-    bo_str2_int[2] = ntohl(str2_int[2]);
-    bo_str2_int[3] = ntohl(str2_int[3]);
-
-    shifted_str2_int[0] = (bo_str2_int[0] << 4) | (bo_str2_int[1] >> 28);
-    shifted_str2_int[1] = (bo_str2_int[1] << 4) | (bo_str2_int[2] >> 28);
-    shifted_str2_int[2] = (bo_str2_int[2] << 4) | (bo_str2_int[3] >> 28);
-    shifted_str2_int[3] = (bo_str2_int[3] << 4) | (bo_str2_int[0] >> 28);
-#endif
     
     contains[str1[0]] = contains[str1[1]] = contains[str1[2]]
         = contains[str1[3]] = contains[str1[4]] = contains[str1[5]]
@@ -201,19 +185,35 @@ int lcs_upper_bound(const uint32_t * const str1_int, const uint32_t * const str2
         + contains[str2[12]] + contains[str2[13]] + contains[str2[14]]
         + contains[str2[15]];
 
-#ifdef DO_SECOND_SUM
-    second_sum = contains[str2_r[0]] + contains[str2_r[1]] + contains[str2_r[2]]
-        + contains[str2_r[3]] + contains[str2_r[4]] + contains[str2_r[5]]
-        + contains[str2_r[6]] + contains[str2_r[7]] + contains[str2_r[8]]
-        + contains[str2_r[9]] + contains[str2_r[10]] + contains[str2_r[11]]
-        + contains[str2_r[12]] + contains[str2_r[13]] + contains[str2_r[14]]
-        + contains[str2_r[15]];
-
-    // can be off up to one nibble (e.g., "1110" and "2111")
-    ret = MAX(first_sum, second_sum) * 2 + 1;
-#else
     // can be off up to two nibbles (e.g., "0110" and "1122")
     ret = first_sum * 2 + 2;
+#ifdef DO_SECOND_SUM
+    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;
+        int second_sum;
+
+        bo_str2_int[0] = ntohl(str2_int[0]);
+        bo_str2_int[1] = ntohl(str2_int[1]);
+        bo_str2_int[2] = ntohl(str2_int[2]);
+        bo_str2_int[3] = ntohl(str2_int[3]);
+
+        shifted_str2_int[0] = (bo_str2_int[0] << 4) | (bo_str2_int[1] >> 28);
+        shifted_str2_int[1] = (bo_str2_int[1] << 4) | (bo_str2_int[2] >> 28);
+        shifted_str2_int[2] = (bo_str2_int[2] << 4) | (bo_str2_int[3] >> 28);
+        shifted_str2_int[3] = (bo_str2_int[3] << 4) | (bo_str2_int[0] >> 28);
+
+        second_sum = contains[str2_r[0]] + contains[str2_r[1]] + contains[str2_r[2]]
+            + contains[str2_r[3]] + contains[str2_r[4]] + contains[str2_r[5]]
+            + contains[str2_r[6]] + contains[str2_r[7]] + contains[str2_r[8]]
+            + contains[str2_r[9]] + contains[str2_r[10]] + contains[str2_r[11]]
+            + contains[str2_r[12]] + contains[str2_r[13]] + contains[str2_r[14]]
+            + contains[str2_r[15]];
+
+        // can be off up to one nibble (e.g., "1110" and "2111")
+        ret = MAX(first_sum, second_sum) * 2 + 1;
+    }
 #endif
 
     contains[str1[0]] = contains[str1[1]] = contains[str1[2]]