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diff --git a/servo/components/style/values/computed/ratio.rs b/servo/components/style/values/computed/ratio.rs
new file mode 100644
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+++ b/servo/components/style/values/computed/ratio.rs
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! `<ratio>` computed values.
+
+use crate::values::animated::{Animate, Procedure};
+use crate::values::computed::NonNegativeNumber;
+use crate::values::distance::{ComputeSquaredDistance, SquaredDistance};
+use crate::values::generics::ratio::Ratio as GenericRatio;
+use crate::{One, Zero};
+use std::cmp::{Ordering, PartialOrd};
+
+/// A computed <ratio> value.
+pub type Ratio = GenericRatio<NonNegativeNumber>;
+
+impl PartialOrd for Ratio {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        f64::partial_cmp(
+            &((self.0).0 as f64 * (other.1).0 as f64),
+            &((self.1).0 as f64 * (other.0).0 as f64),
+        )
+    }
+}
+
+/// https://drafts.csswg.org/css-values/#combine-ratio
+impl Animate for Ratio {
+    fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
+        // If either <ratio> is degenerate, the values cannot be interpolated.
+        if self.is_degenerate() || other.is_degenerate() {
+            return Err(());
+        }
+
+        // Addition of <ratio>s is not possible, and based on
+        // https://drafts.csswg.org/css-values-4/#not-additive,
+        // we simply use the first value as the result value.
+        // Besides, the procedure for accumulation should be identical to addition here.
+        if matches!(procedure, Procedure::Add | Procedure::Accumulate { .. }) {
+            return Ok(self.clone());
+        }
+
+        // The interpolation of a <ratio> is defined by converting each <ratio> to a number by
+        // dividing the first value by the second (so a ratio of 3 / 2 would become 1.5), taking
+        // the logarithm of that result (so the 1.5 would become approximately 0.176), then
+        // interpolating those values.
+        //
+        // The result during the interpolation is converted back to a <ratio> by inverting the
+        // logarithm, then interpreting the result as a <ratio> with the result as the first value
+        // and 1 as the second value.
+        let start = self.to_f32().ln();
+        let end = other.to_f32().ln();
+        let e = std::f32::consts::E;
+        let result = e.powf(start.animate(&end, procedure)?);
+        // The range of the result is [0, inf), based on the easing function.
+        if result.is_zero() || result.is_infinite() {
+            return Err(());
+        }
+        Ok(Ratio::new(result, 1.0f32))
+    }
+}
+
+impl ComputeSquaredDistance for Ratio {
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        if self.is_degenerate() || other.is_degenerate() {
+            return Err(());
+        }
+        // Use the distance of their logarithm values. (This is used by testing, so don't need to
+        // care about the base. Here we use the same base as that in animate().)
+        self.to_f32()
+            .ln()
+            .compute_squared_distance(&other.to_f32().ln())
+    }
+}
+
+impl Zero for Ratio {
+    fn zero() -> Self {
+        Self::new(Zero::zero(), One::one())
+    }
+
+    fn is_zero(&self) -> bool {
+        self.0.is_zero()
+    }
+}
+
+impl Ratio {
+    /// Returns a new Ratio.
+    #[inline]
+    pub fn new(a: f32, b: f32) -> Self {
+        GenericRatio(a.into(), b.into())
+    }
+
+    /// Returns the used value. A ratio of 0/0 behaves as the ratio 1/0.
+    /// https://drafts.csswg.org/css-values-4/#ratios
+    pub fn used_value(self) -> Self {
+        if self.0.is_zero() && self.1.is_zero() {
+            Ratio::new(One::one(), Zero::zero())
+        } else {
+            self
+        }
+    }
+
+    /// Returns true if this is a degenerate ratio.
+    /// https://drafts.csswg.org/css-values/#degenerate-ratio
+    #[inline]
+    pub fn is_degenerate(&self) -> bool {
+        self.0.is_zero() || self.1.is_zero()
+    }
+
+    /// Returns the f32 value by dividing the first value by the second one.
+    #[inline]
+    fn to_f32(&self) -> f32 {
+        debug_assert!(!self.is_degenerate());
+        (self.0).0 / (self.1).0
+    }
+}