1 files changed, 2 insertions, 2 deletions
diff --git a/js/util.js b/js/util.js
index cdabbe1..f2fd129 100644
--- a/js/util.js
+++ b/js/util.js
@@ -58,8 +58,8 @@ 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 mod(n,m){ return n-(m * floor(n/m)) }
-function modi(n,m){ return floor(n-(m * floor(n/m))) }
+function mod(n,m){ n = n % m; return n < 0 ? (m + n) : n }
+function modi(n,m){ return floor(mod(n,m)) }
 function dist(x0,y0,x1,y1){ return sqrt(pow(x1-x0,2)+pow(y1-y0,2)) }
 function angle(x0,y0,x1,y1){ return atan2(y1-y0,x1-x0) }
 function avg(m,n,a){ return (m*(a-1)+n)/a }