1 files changed, 1 insertions, 0 deletions
diff --git a/js/util.js b/js/util.js
index 948b3f6..b728377 100644
--- a/js/util.js
+++ b/js/util.js
@@ -42,6 +42,7 @@ function randint(n){ return rand(n)|0 }
 function choice(a){ return a[randint(a.length)] }
 function deg(n){ return n*180/PI }
 function rad(n){ return n*PI/180 }
+function xor(a,b){ a=!!a; b=!!b; return (a||b) && !(a&&b) }
 function pixel(x,y){ return 4*(mod(y,h)*w+mod(x,w)) }
 function rgbpixel(d,x,y){
   var p = pixel(~~x,~~y)