From e799bc169a644517fc2fe77783392259c555fac5 Mon Sep 17 00:00:00 2001
From: Alex 'AdUser' Z <ad_user@runbox.com>
Date: Wed, 2 Apr 2014 16:47:49 +1100
Subject: [PATCH] * bitmap compare with dictionary

---
 src/bitmap.c | 24 ++++++++++++++++++++++++
 src/bitmap.h |  1 +
 2 files changed, 25 insertions(+)

diff --git a/src/bitmap.c b/src/bitmap.c
index f4797cf..7b80602 100644
--- a/src/bitmap.c
+++ b/src/bitmap.c
@@ -17,6 +17,27 @@
 #include "main.h"
 #include "bitmap.h"
 
+unsigned char dict[256] = {
+/* 0x00 _0 _1 _2 _3 _4 _5 _6 _7 _8 _9 _A _B _C _D _E _F */
+/* ---------------------------------------------------- */
+/* 0_ */ 0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
+/* 1_ */ 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
+/* 2_ */ 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
+/* 3_ */ 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
+/* 4_ */ 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
+/* 5_ */ 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
+/* 6_ */ 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
+/* 7_ */ 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
+/* 8_ */ 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
+/* 9_ */ 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
+/* A_ */ 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
+/* B_ */ 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
+/* C_ */ 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
+/* D_ */ 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
+/* E_ */ 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
+/* F_ */ 4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8,
+};
+
 int bitmap_compare(const unsigned char *a, const unsigned char *b)
 {
   unsigned char diff = 0;
@@ -25,10 +46,13 @@ int bitmap_compare(const unsigned char *a, const unsigned char *b)
 
   for (i = 0; i < BITMAP_SIZE; i++, a++, b++) {
     diff = *a ^ *b;
+/* bruteforce:
     while (diff) {
       cnt += (diff & 1);
       diff >>= 1;
     }
+*/
+    cnt += dict[diff];
   }
 
   return cnt;
diff --git a/src/bitmap.h b/src/bitmap.h
index 981b22b..f7989bf 100644
--- a/src/bitmap.h
+++ b/src/bitmap.h
@@ -5,5 +5,6 @@
 typedef unsigned char bitmap_t[BITMAP_SIZE];
 
 int bitmap_compare(const unsigned char *a, const unsigned char *b);
+
 #endif
 #define HAS_BITMAP_H 1