UAS2.0_DEV_TEST/ext/modern/theme-base/sass/etc/functions/calc-math.scss

@function calc-sum($one, $two) {
    @if $one != null and $two != null {
        @if $one == 0 {
            @return $two;
        }

        @if $two == 0 {
            @return $one;
        }

        // TODO if units are the same no need to use calc

        @return calc(#{$one} + #{$two});
    }

    @if $one != null {
        @return $one;
    }

    @if $two != null {
        @return $two;
    }

    @return null;
}

@function calc-diff($one, $two) {
    @if $one != null and $two != null {
        @if $one == 0 {
            @return $two;
        }

        @if $two == 0 {
            @return $one;
        }

        // TODO if units are the same no need to use calc

        @return calc(#{$one} - #{$two});
    }

    @if $one != null {
        @return $one;
    }

    @if $two != null {
        @return $two;
    }

    @return null;
}

@function add-if ($value1, $value2) {
    @if $value1 == null or $value2 == null {
        @return null;
    }

    @return $value1 + $value2;
}