diff --git a/lib/log2.asm b/lib/log2.asm
index cdc2bb8..b61dbd9 100644
--- a/lib/log2.asm
+++ b/lib/log2.asm
@@ -3,12 +3,13 @@
 ; OUT	AX	dual logarithm
 log2:
   push cx
-  mov cx, 16
+  mov cx, 15
 .loop:
-  sar ax, 1
-  loopnz .loop
-  xchg ax, cx
+  rcl ax, 1
+  jc .ret
+  loop .loop
+.ret:
+  cmc
+  mov ax, cx
   pop cx
-  neg ax
-  add ax, 15
   ret