Bug 788701 - Decrease the length of the text to match when there is a start position. r=jorendorff

js/src/jit-test/tests/basic/string-contains.js

@@ -40,3 +40,7 @@ var idx = {valueOf : (function () {
 })};
 myobj.contains("elephant", idx);
 assertEq(gotPos, true);
+assertEq("xyzzy".contains("zy\0", 2), false);
+var dots = Array(10000).join('.');
+assertEq(dots.contains("\x01", 10000), false);
+assertEq(dots.contains("\0", 10000), false);

js/src/jsstr.cpp

@@ -1160,7 +1160,9 @@ str_contains(JSContext *cx, unsigned argc, Value *vp)
             return false;
 
         // Step 6
-        text += uint32_t(Min(double(textlen), Max(0.0, posDouble)));
+        uint32_t delta = uint32_t(Min(double(textlen), Max(0.0, posDouble)));
+        text += delta;
+        textlen -= delta;
     }
 
     // Step 7