src/css/adjustCSS.js

define( [

    "../core",

    "../var/rcssNum"

], function( jQuery, rcssNum ) {

"use strict";

function adjustCSS( elem, prop, valueParts, tween ) {

    var adjusted,

        scale = 1,

        maxIterations = 20,

        currentValue = tween ?

            function() {

                return tween.cur();

            } :

            function() {

                return jQuery.css( elem, prop, "" );

            },

        initial = currentValue(),

        unit = valueParts && valueParts[ 3 ] || ( jQuery.cssNumber[ prop ] ? "" : "px" ),

        // Starting value computation is required for potential unit mismatches

        initialInUnit = ( jQuery.cssNumber[ prop ] || unit !== "px" && +initial ) &&

            rcssNum.exec( jQuery.css( elem, prop ) );

    if ( initialInUnit && initialInUnit[ 3 ] !== unit ) {

        // Trust units reported by jQuery.css

        unit = unit || initialInUnit[ 3 ];

        // Make sure we update the tween properties later on

        valueParts = valueParts || [];

        // Iteratively approximate from a nonzero starting point

        initialInUnit = +initial || 1;

        do {

            // If previous iteration zeroed out, double until we get *something*.

            // Use string for doubling so we don't accidentally see scale as unchanged below

            scale = scale || ".5";

            // Adjust and apply

            initialInUnit = initialInUnit / scale;

            jQuery.style( elem, prop, initialInUnit + unit );

        // Update scale, tolerating zero or NaN from tween.cur()

        // Break the loop if scale is unchanged or perfect, or if we've just had enough.

        } while (

            scale !== ( scale = currentValue() / initial ) && scale !== 1 && --maxIterations

        );

    }

    if ( valueParts ) {

        initialInUnit = +initialInUnit || +initial || 0;

        // Apply relative offset (+=/-=) if specified

        adjusted = valueParts[ 1 ] ?

            initialInUnit + ( valueParts[ 1 ] + 1 ) * valueParts[ 2 ] :

            +valueParts[ 2 ];

        if ( tween ) {

            tween.unit = unit;

            tween.start = initialInUnit;

            tween.end = adjusted;

        }

    }

    return adjusted;

}

return adjustCSS;

} );