Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.5)
// Compass (v1.0.1)
// ----

// TEST
$debug:null;

@function compress($value) {
  $top: nth($value, 1);
  $right: nth($value, 2);
  $bottom: nth($value, 3);
  $left: nth($value, 4);
  
  $debug: #{$top}#{$right}#{$bottom}#{$left} !global; 
  $result: null;
  
  // All same
  @if $top == $right and $right == $bottom and $bottom == $left {
     $result: $top;
  // top + bottom same
  } @else if $top == $bottom {
      @if $right == $left  {
        // left + right same
        $result: #{$top} #{$right};
      }
  }@else if $right == $left {
    $result: #{$top} #{$right} #{$bottom};
  } @else {
    $result: $value;
  }
  @return $result;
}

.all-different {
  padding: compress(1px 2px 3px 4px);
}

.vertical-horizontal {
  padding: compress(1px 2px 1px 2px);
}

.top-horizontal-bottom {
  padding: compress(1px 2px 3px 2px);
}

SassMeister-output.css

.all-different {
  padding: 1px 2px 3px 4px;
}

.vertical-horizontal {
  padding: 1px 2px;
}

.top-horizontal-bottom {
  padding: 1px 2px 3px;
}