update edge case behavior; a function with f(l)===0 or f(h)===0 will …

…yield

an interval beginning with l or ending with h.

index.js

@@ -1,40 +1,49 @@
 /* Copyright 2016 Paul Brewer, Economic & Financial Technology COnsulting LLC  <drpaulbrewer@eaftc.com> */
 /* License: MIT https://opensource.org/licenses/MIT  */
 
-module.exports = function(l,h,tol,f){
-    'use strict';
-    // returns a two element array giving an inclusive range of zero values of f
-    // requires strictly everywhere non-descending function f
-    // use with caution:  this code assumes but does and can not check that f is everywhere non-descending
-    var right=h,left=l,intflag=(tol>=1);
-    var fl = f(l), fh=f(h);
-    if ((fl===0) && (fh===0)) return [l,h];
-    if (fh<fl) throw new Error("findZeroRange: requires non-descending function");
-    if (fl>=0) return [];
-    if (fh<=0) return [];
-    var zleft,zright,mid;
-    zright=left;
-    while ((right-zright)>tol){
-	mid = (right+zright)/2;
-	if (intflag) mid = Math.floor(mid);
-	if (f(mid)>0)
-	    right =  mid;
-	else 
-	    zright = mid;
+module.exports = function (l, h, tol, f) {
+  'use strict';
+  // returns a two element array giving an inclusive range of zero values of f
+  // requires strictly everywhere non-descending function f
+  // use with caution:  this code assumes but does and can not check that f is everywhere non-descending
+  var right = h,
+    left = l,
+    intflag = (tol >= 1);
+  var fl = f(l),
+    fh = f(h);
+  if ((fl === 0) && (fh === 0)) return [l, h];
+  if (fh < fl) throw new Error("findZeroRange: requires non-descending function");
+  if (fl > 0) return [];
+  if (fh < 0) return [];
+  var zleft, zright, mid;
+  zright = left;
+  if (fh===0){
+    zright = right;
+  } else {
+    while ((right - zright) > tol) {
+      mid = (right + zright) / 2;
+      if (intflag) mid = Math.floor(mid);
+      if (f(mid) > 0)
+        right = mid;
+      else
+        zright = mid;
     }
-    if (f(zright)<0)
-	return [zright];
-    zleft=zright;
-    while ((zleft-left)>tol){
-	mid = (left+zleft)/2;
-	if (intflag) mid = Math.floor(mid);
-	if (f(mid)<0)
-	    left = mid;
-	else
-	    zleft = mid;
+    if (f(zright) < 0)
+      return [zright];
+  }
+  if (fl===0){
+    zleft = l;
+  } else {
+    zleft = zright;
+    while ((zleft - left) > tol) {
+      mid = (left + zleft) / 2;
+      if (intflag) mid = Math.floor(mid);
+      if (f(mid) < 0)
+        left = mid;
+      else
+        zleft = mid;
     }
-    if (zleft===zright) return [zright];
-    return [zleft, zright];
+  }
+  if (zleft === zright) return [zright];
+  return [zleft, zright];
 };
-
-