Font-Awesome/scss/_rotated-flipped.scss

// rotated and flipped icons
// -------------------------

$rotations-requiring-ie-fix: (
  "flip-horizontal",
  "flip-vertical"
);
$rotation-selector: '';

// calculate classes and values for rotation
@for $i from 0 through 359 {
  @if $i == 0 or $i % $fa-rotation-increment == 0 {
    $rotation-selector: #{$fa-css-prefix}-rotate-#{$i};

    .#{$rotation-selector} {
      @include fa-icon-rotate($i);
    }
    // check if this item needs some ie love
    @if $i == 0 or $i % 90 == 0 {
      $rotations-requiring-ie-fix: append($rotations-requiring-ie-fix, #{$rotation-selector});
    }
  }
}

// flip icons horizontal/vertical
.#{$fa-css-prefix}-flip-horizontal { @include fa-icon-flip(-1, 1, 0); }
.#{$fa-css-prefix}-flip-vertical   { @include fa-icon-flip(1, -1, 2); }

// ie 8-9 fix
// -------------------------
// todo: check on assigning an array of selectors to the selector instead of using
//       this loop

:root  {
  @each $fix in $rotations-requiring-ie-fix {
    .#{$fix} {
      filter: none;
    }
  }
}