fix bug & intrinsic log

1 files changed, 12 insertions, 1 deletions

diff --git a/magic_buddy/magic_buddy.c b/magic_buddy/magic_buddy.c
index 1eb2d8f..1029f58 100644
--- a/magic_buddy/magic_buddy.c
+++ b/magic_buddy/magic_buddy.c
@@ -1,6 +1,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <assert.h>
+#include <math.h>
 #include "magic_buddy.h"
 
 struct free_block {
@@ -11,11 +12,21 @@ struct free_block {
 };
 
 // log2 of size rounded up (ceil) or down (!ceil) to the nearest power of 2
+// https://stackoverflow.com/questions/11376288/fast-computing-of-log2-for-64-bit-integers
 static size_t size2log(size_t size, int ceil) {
+#if 1
+    size_t floor_log
+        = (8*sizeof(unsigned long long))
+        - __builtin_clzll((unsigned long long)size) - 1;
+    if (!size) floor_log = 0;
+    return (ceil && (size > (1 << floor_log))) ? (floor_log + 1) : floor_log;
+#else
     size_t floor_log = 0;
     for (size_t i = 0; i < (8 * sizeof(size)); i++)
-        if (size & (1 << i)) floor_log = i;
+        if (size & (1ul << i)) floor_log = i;
+
     return (ceil && (size > (1 << floor_log))) ? (floor_log + 1) : floor_log;
+#endif
 }
 
 static struct free_block *buddy_of(struct free_block *block, size_t logsize,