function extractNumber(obj, decimalPlaces, allowNegative) {
    var temp = obj.value;

    // avoid changing things if already formatted correctly
    var reg0Str = '[0-9]*';
    if (decimalPlaces > 0) {
        reg0Str += '\\.?[0-9]{0,' + decimalPlaces + '}';
    } else if (decimalPlaces < 0) {
        reg0Str += '\\.?[0-9]*';
    }
    reg0Str = allowNegative ? '^-?' + reg0Str : '^' + reg0Str;
    reg0Str = reg0Str + '$';
    var reg0 = new RegExp(reg0Str);
    if (reg0.test(temp)) return true;

    // first replace all non numbers
    var reg1Str = '[^0-9' + (decimalPlaces != 0 ? '.' : '') + (allowNegative ? '-' : '') + ']';
    var reg1 = new RegExp(reg1Str, 'g');
    temp = temp.replace(reg1, '');

    if (allowNegative) {
        // replace extra negative
        var hasNegative = temp.length > 0 && temp.charAt(0) == '-';
        var reg2 = /-/g;
        temp = temp.replace(reg2, '');
        if (hasNegative) temp = '-' + temp;
    }

    if (decimalPlaces != 0) {
        var reg3 = /\./g;
        var reg3Array = reg3.exec(temp);
        if (reg3Array != null) {
            // keep only first occurrence of .
            //  and the number of places specified by decimalPlaces or the entire string if decimalPlaces < 0
            var reg3Right = temp.substring(reg3Array.index + reg3Array[0].length);
            reg3Right = reg3Right.replace(reg3, '');
            reg3Right = decimalPlaces > 0 ? reg3Right.substring(0, decimalPlaces) : reg3Right;
            temp = temp.substring(0, reg3Array.index) + '.' + reg3Right;
        }
    }

    obj.value = temp;
}
function blockNonNumbers(obj, e, allowDecimal, allowNegative) {
    var key;
    var isCtrl = false;
    var keychar;
    var reg;

    if (window.event) {
        key = e.keyCode;
        isCtrl = window.event.ctrlKey
    }
    else if (e.which) {
        key = e.which;
        isCtrl = e.ctrlKey;
    }

    if (isNaN(key)) return true;

    keychar = String.fromCharCode(key);

    // check for backspace or delete, or if Ctrl was pressed
    if (key == 8 || isCtrl) {
        return true;
    }

    reg = /\d/;
    var isFirstN = allowNegative ? keychar == '-' && obj.value.indexOf('-') == -1 : false;
    var isFirstD = allowDecimal ? keychar == '.' && obj.value.indexOf('.') == -1 : false;

    return isFirstN || isFirstD || reg.test(keychar);
}

function alerta(mensaje) {
    alert(mensaje);
}

function openimgs(id) {
    window.open('imagenes.aspx?id=' + id, 'imagenes', 'width=600,height=600,left=' + (screen.availWidth / 2 - 300) + ',top=' + (screen.availHeight / 2 - 300) + '');
}