Introduce codecs for facet types (string, f64, u64, i64)

src/facet/facet_type.rs

@@ -0,0 +1,15 @@
+use std::cmp;
+
+#[derive(Debug, Copy, Clone, PartialOrd, Ord, PartialEq, Eq, Hash)]
+pub enum FacetType {
+    String,
+    F64,
+    I64,
+    U64,
+}
+
+impl FacetType {
+    pub fn merge(a: FacetType, b: FacetType) -> FacetType {
+        cmp::min(a, b)
+    }
+}

src/facet/mod.rs

@@ -0,0 +1,4 @@
+mod facet_type;
+pub mod value_encoding;
+
+pub use self::facet_type::FacetType;

src/facet/value_encoding.rs

@@ -0,0 +1,89 @@
+// https://stackoverflow.com/a/43305015/1941280
+#[inline]
+pub fn f64_into_bytes(float: f64) -> Option<[u8; 8]> {
+    if float.is_finite() {
+        if float == 0.0 || float == -0.0 {
+            return Some(xor_first_bit(0.0_f64.to_be_bytes()));
+        } else if float.is_sign_negative() {
+            return Some(xor_all_bits(float.to_be_bytes()));
+        } else if float.is_sign_positive() {
+            return Some(xor_first_bit(float.to_be_bytes()));
+        }
+    }
+    None
+}
+
+#[inline]
+pub fn u64_into_bytes(int: u64) -> [u8; 8] {
+    int.to_be_bytes()
+}
+
+#[inline]
+pub fn u64_from_bytes(bytes: [u8; 8]) -> u64 {
+    u64::from_be_bytes(bytes)
+}
+
+#[inline]
+pub fn i64_into_bytes(int: i64) -> [u8; 8] {
+    xor_first_bit(int.to_be_bytes())
+}
+
+#[inline]
+pub fn i64_from_bytes(bytes: [u8; 8]) -> i64 {
+    i64::from_be_bytes(xor_first_bit(bytes))
+}
+
+#[inline]
+fn xor_first_bit(mut x: [u8; 8]) -> [u8; 8] {
+    x[0] ^= 0x80;
+    x
+}
+
+#[inline]
+fn xor_all_bits(mut x: [u8; 8]) -> [u8; 8] {
+    x.iter_mut().for_each(|b| *b ^= 0xff);
+    x
+}
+
+#[cfg(test)]
+mod tests {
+    use std::cmp::Ordering::Less;
+    use super::*;
+
+    fn is_sorted<T: Ord>(x: &[T]) -> bool {
+        x.windows(2).map(|x| x[0].cmp(&x[1])).all(|o| o == Less)
+    }
+
+    #[test]
+    fn ordered_f64_bytes() {
+        let a = -13_f64;
+        let b = -10.0;
+        let c = -0.0;
+        let d =  1.0;
+        let e =  43.0;
+
+        let vec: Vec<_> = [a, b, c, d, e].iter().cloned().map(f64_into_bytes).collect();
+        assert!(is_sorted(&vec), "{:?}", vec);
+    }
+
+    #[test]
+    fn ordered_u64_bytes() {
+        let a = 0_u64;
+        let b = 1_u64;
+        let c = 43_u64;
+
+        let vec: Vec<_> = [a, b, c].iter().cloned().map(u64_into_bytes).collect();
+        assert!(is_sorted(&vec), "{:?}", vec);
+    }
+
+    #[test]
+    fn ordered_i64_bytes() {
+        let a = -10_i64;
+        let b = -0_i64;
+        let c =  1_i64;
+        let d =  43_i64;
+
+        let vec: Vec<_> = [a, b, c, d].iter().cloned().map(i64_into_bytes).collect();
+        assert!(is_sorted(&vec), "{:?}", vec);
+    }
+}