chore: checkpoint before Python removal

vendor/minimal-lexical/src/extended_float.rs

@@ -0,0 +1,24 @@
+// FLOAT TYPE
+
+#![doc(hidden)]
+
+use crate::num::Float;
+
+/// Extended precision floating-point type.
+///
+/// Private implementation, exposed only for testing purposes.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct ExtendedFloat {
+    /// Mantissa for the extended-precision float.
+    pub mant: u64,
+    /// Binary exponent for the extended-precision float.
+    pub exp: i32,
+}
+
+/// Converts an `ExtendedFloat` to the closest machine float type.
+#[inline(always)]
+pub fn extended_to_float<F: Float>(x: ExtendedFloat) -> F {
+    let mut word = x.mant;
+    word |= (x.exp as u64) << F::MANTISSA_SIZE;
+    F::from_bits(word)
+}