Slider: Fix max calculation, when step is float

Fixes #10721
Closes gh-1398
(cherry picked from commit ae1d6d5)

tests/unit/slider/slider_options.js

@@ -40,7 +40,7 @@ test( "disabled", function(){
 });
 
 test( "max", function() {
-	expect( 4 );
+	expect( 5 );
 	element = $( "<div></div>" );
 
 	options = {
@@ -72,6 +72,18 @@ test( "max", function() {
 	ok( element.slider( "value" ) === options.max, "value method will max, step is changed" );
 	element.slider( "destroy" );
 
+	options = {
+		max: 60,
+		min: 50,
+		orientation: "horizontal",
+		step: 0.1,
+		value: 60
+	};
+
+	element.slider( options );
+	ok( element.slider( "value" ) === options.max, "value method will max, step is changed and step is float" );
+	element.slider( "destroy" );
+
 });
 
 test( "min", function() {

ui/slider.js

@@ -547,8 +547,26 @@ return $.widget( "ui.slider", $.ui.mouse, {
 	},
 
 	_calculateNewMax: function() {
-		var remainder = ( this.options.max - this._valueMin() ) % this.options.step;
-		this.max = this.options.max - remainder;
+		var max = this.options.max,
+			min = this._valueMin(),
+			step = this.options.step,
+			aboveMin = Math.floor( ( max - min ) / step ) * step;
+		max = aboveMin + min;
+		this.max = parseFloat( max.toFixed( this._precision() ) );
+	},
+
+	_precision: function() {
+		var precision = this._precisionOf( this.options.step );
+		if ( this.options.min !== null ) {
+			precision = Math.max( precision, this._precisionOf( this.options.min ) );
+		}
+		return precision;
+	},
+
+	_precisionOf: function( num ) {
+		var str = num.toString(),
+			decimal = str.indexOf( "." );
+		return decimal === -1 ? 0 : str.length - decimal - 1;
 	},
 
 	_valueMin: function() {