Simplify and comment a bit

Author: gbrail

rhino/src/main/java/org/mozilla/javascript/NativeNumber.java

@@ -148,12 +148,7 @@ private static Object js_toFixed(
             int precisionMin = cx.version < Context.VERSION_ES6 ? -20 : 0;
             /* We allow a larger range of precision than
             ECMA requires; this is permitted by ECMA. */
-            if (p < precisionMin || p > MAX_PRECISION) {
-                String msg =
-                        ScriptRuntime.getMessageById(
-                                "msg.bad.precision", ScriptRuntime.toString(args[0]));
-                throw ScriptRuntime.rangeError(msg);
-            }
+            checkPrecision(p, precisionMin, args[0]);
             fractionDigits = ScriptRuntime.toInt32(p);
         } else {
             fractionDigits = 0;
@@ -182,13 +177,7 @@ private static Object js_toExponential(
         if (!Double.isFinite(value)) {
             return ScriptRuntime.toString(value);
         }
-
-        if (p < 0.0 || p > MAX_PRECISION) {
-            String msg =
-                    ScriptRuntime.getMessageById(
-                            "msg.bad.precision", ScriptRuntime.toString(args[0]));
-            throw ScriptRuntime.rangeError(msg);
-        }
+        checkPrecision(p, 0.0, args.length > 0 ? args[0] : Undefined.instance);
 
         // Trigger the special handling for undefined, which requires that
         // we hold off on this bit until the checks above,.
@@ -209,17 +198,20 @@ private static Object js_toPrecision(
         if (!Double.isFinite(value)) {
             return ScriptRuntime.toString(value);
         }
-        if (p < 1 || p > MAX_PRECISION) {
-            String msg =
-                    ScriptRuntime.getMessageById(
-                            "msg.bad.precision", ScriptRuntime.toString(args[0]));
-            throw ScriptRuntime.rangeError(msg);
-        }
+        checkPrecision(p, 1.0, args[0]);
         int precision = ScriptRuntime.toInt32(p);
 
         return DecimalFormatter.toPrecision(value, precision);
     }
 
+    private static void checkPrecision(double p, double min, Object arg) {
+        if (p < min || p > MAX_PRECISION) {
+            String msg =
+                    ScriptRuntime.getMessageById("msg.bad.precision", ScriptRuntime.toString(arg));
+            throw ScriptRuntime.rangeError(msg);
+        }
+    }
+
     private static NativeNumber toSelf(Scriptable thisObj) {
         return LambdaConstructor.convertThisObject(thisObj, NativeNumber.class);
     }

rhino/src/main/java/org/mozilla/javascript/dtoa/DecimalFormatter.java

@@ -26,10 +26,7 @@ public static String toExponential(double v, int fractionDigits) {
         if (negative) {
             val = Math.abs(v);
         }
-        BigDecimal bd = new BigDecimal(val, MathContext.UNLIMITED);
-        if (bd.precision() > fractionDigits + 1) {
-            bd = bd.round(new MathContext(fractionDigits + 1, RoundingMode.HALF_UP));
-        }
+        var bd = new BigDecimal(val, new MathContext(fractionDigits + 1, RoundingMode.HALF_UP));
 
         int exponent;
         if (bd.scale() >= 0) {
@@ -72,10 +69,7 @@ public static String toPrecision(double v, int precision) {
         } else {
             val = v;
         }
-        var bd = new BigDecimal(val, MathContext.UNLIMITED);
-        if (bd.precision() > precision) {
-            bd = bd.round(new MathContext(precision, RoundingMode.HALF_UP));
-        }
+        var bd = new BigDecimal(val, new MathContext(precision, RoundingMode.HALF_UP));
 
         int scale = bd.scale();
         int numDigits = bd.precision();

rhino/src/main/java/org/mozilla/javascript/dtoa/DoubleFormatter.java

@@ -97,7 +97,13 @@ public static String toString(double v) {
         return bits > 0 ? "Infinity" : "-Infinity";
     }
 
+    /**
+     * Convert a double to a Decimal object that may be output in various ways. Unlike toString, and
+     * since it always returns a Decimal, it must be used with finite numbers only or the result is
+     * undetermined.
+     */
     public static Decimal toDecimal(double v) {
+        assert Double.isFinite(v);
         long bits = Double.doubleToRawLongBits(v);
         long t = bits & T_MASK;
         int bq = (int) (bits >>> (P - 1)) & BQ_MASK;