1 files changed, 26 insertions, 0 deletions
diff --git a/pk/strlen.c b/pk/strlen.c
new file mode 100644
index 0000000..f600d47
--- /dev/null
+++ b/pk/strlen.c
@@ -0,0 +1,26 @@
+#include <string.h>
+#include <stdlib.h>
+
+// from http://www-graphics.stanford.edu/~seander/bithacks.html
+static inline long hasZeroByte(long l)
+{
+  if(sizeof(long) == 4)
+    return (l - 0x01010101UL) & ~l & 0x80808080UL;
+  else if(sizeof(long) == 8)
+    return (l - 0x0101010101010101UL) & ~l & 0x8080808080808080UL;
+}
+
+size_t strlen(const char* s)
+{
+  size_t i = 0;
+
+  // use optimized version if string starts on a long boundary
+  if(((long)s & (sizeof(long)-1)) == 0)
+    while(!hasZeroByte(*(long*)(s+i)))
+      i += sizeof(long);
+
+  while(s[i])
+    i++;
+
+  return i;
+}