move minmax to bitpacker

move minmax to bitpacker
use minmax in blocked bitpacker

bitpacker/src/blocked_bitpacker.rs

@@ -1,4 +1,4 @@
-use crate::BitUnpacker;
+use crate::{minmax, BitUnpacker};
 
 use super::{bitpacker::BitPacker, compute_num_bits};
 
@@ -83,14 +83,9 @@ impl BlockedBitpacker {
     }
 
     pub fn flush(&mut self) {
-        if let Some(min_value) = self.buffer.iter().min() {
+        if let Some((min_value, max_value)) = minmax(self.buffer.iter()) {
             let mut bit_packer = BitPacker::new();
-            let num_bits_block = self
-                .buffer
-                .iter()
-                .map(|val| compute_num_bits(*val - min_value))
-                .max()
-                .unwrap();
+            let num_bits_block = compute_num_bits(*max_value - min_value);
             // todo performance: the padding handling could be done better, e.g. use a slice and
             // return num_bytes written from bitpacker
             self.compressed_blocks

bitpacker/src/lib.rs

@@ -37,3 +37,16 @@ pub fn compute_num_bits(n: u64) -> u8 {
         64
     }
 }
+
+pub fn minmax<I, T>(mut vals: I) -> Option<(T, T)>
+where
+    I: Iterator<Item = T>,
+    T: Copy + Ord,
+{
+    if let Some(first_el) = vals.next() {
+        return Some(vals.fold((first_el, first_el), |(min_val, max_val), el| {
+            (min_val.min(el), max_val.max(el))
+        }));
+    }
+    None
+}