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diff --git a/third_party/rust/serde_json/src/lexical/cached.rs b/third_party/rust/serde_json/src/lexical/cached.rs
new file mode 100644
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+++ b/third_party/rust/serde_json/src/lexical/cached.rs
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+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Cached powers trait for extended-precision floats.
+
+use super::cached_float80;
+use super::float::ExtendedFloat;
+
+// POWERS
+
+/// Precalculated powers that uses two-separate arrays for memory-efficiency.
+#[doc(hidden)]
+pub(crate) struct ExtendedFloatArray {
+    // Pre-calculated mantissa for the powers.
+    pub mant: &'static [u64],
+    // Pre-calculated binary exponents for the powers.
+    pub exp: &'static [i32],
+}
+
+/// Allow indexing of values without bounds checking
+impl ExtendedFloatArray {
+    #[inline]
+    pub fn get_extended_float(&self, index: usize) -> ExtendedFloat {
+        let mant = self.mant[index];
+        let exp = self.exp[index];
+        ExtendedFloat { mant, exp }
+    }
+
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.mant.len()
+    }
+}
+
+// MODERATE PATH POWERS
+
+/// Precalculated powers of base N for the moderate path.
+#[doc(hidden)]
+pub(crate) struct ModeratePathPowers {
+    // Pre-calculated small powers.
+    pub small: ExtendedFloatArray,
+    // Pre-calculated large powers.
+    pub large: ExtendedFloatArray,
+    /// Pre-calculated small powers as 64-bit integers
+    pub small_int: &'static [u64],
+    // Step between large powers and number of small powers.
+    pub step: i32,
+    // Exponent bias for the large powers.
+    pub bias: i32,
+}
+
+/// Allow indexing of values without bounds checking
+impl ModeratePathPowers {
+    #[inline]
+    pub fn get_small(&self, index: usize) -> ExtendedFloat {
+        self.small.get_extended_float(index)
+    }
+
+    #[inline]
+    pub fn get_large(&self, index: usize) -> ExtendedFloat {
+        self.large.get_extended_float(index)
+    }
+
+    #[inline]
+    pub fn get_small_int(&self, index: usize) -> u64 {
+        self.small_int[index]
+    }
+}
+
+// CACHED EXTENDED POWERS
+
+/// Cached powers as a trait for a floating-point type.
+pub(crate) trait ModeratePathCache {
+    /// Get cached powers.
+    fn get_powers() -> &'static ModeratePathPowers;
+}
+
+impl ModeratePathCache for ExtendedFloat {
+    #[inline]
+    fn get_powers() -> &'static ModeratePathPowers {
+        cached_float80::get_powers()
+    }
+}