feat: differential delta fast inverse delta (#18)

Author: jjcfrancisco

src/integer_compression/differential/mod.rs

@@ -0,0 +1,57 @@
+use std::ops::{Add, AddAssign};
+
+pub struct Delta;
+
+impl Delta {
+    pub fn new() -> Delta {
+        Delta
+    }
+
+    // C++ port as it supports any type of numeric data
+    // source: https://github.com/fast-pack/FastPFor/blob/49d44d94773518ef26486f7a58f8da08e8a498bb/headers/deltautil.h#L274
+    pub fn fast_inverse_delta<T>(data: &mut [T])
+    where
+        T: Copy + Add<Output = T> + AddAssign,
+    {
+        if data.is_empty() {
+            return;
+        }
+
+        let sz0 = (data.len() / 4) * 4;
+        let mut i = 1;
+
+        if sz0 >= 4 {
+            let mut a = data[0];
+            while i < sz0 - 4 {
+                a = {
+                    data[i] += a;
+                    data[i]
+                };
+                a = {
+                    data[i + 1] += a;
+                    data[i + 1]
+                };
+                a = {
+                    data[i + 2] += a;
+                    data[i + 2]
+                };
+                a = {
+                    data[i + 3] += a;
+                    data[i + 3]
+                };
+                i += 4;
+            }
+        }
+
+        while i < data.len() {
+            data[i] += data[i - 1];
+            i += 1;
+        }
+    }
+}
+
+impl Default for Delta {
+    fn default() -> Self {
+        Delta::new()
+    }
+}

src/integer_compression/mod.rs

@@ -1,6 +1,7 @@
 pub mod bitpacking;
 pub mod codec;
 pub mod composition;
+pub mod differential;
 pub mod fastpfor;
 pub mod helpers;
 pub mod integer_codec;

src/lib.rs

@@ -7,6 +7,7 @@ pub use error::{FastPForError, FastPForResult};
 pub use integer_compression::bitpacking::{fast_pack, fast_unpack};
 pub use integer_compression::codec::Codec;
 pub use integer_compression::composition::Composition;
+pub use integer_compression::differential::Delta;
 pub use integer_compression::fastpfor::{
     FastPFOR, BLOCK_SIZE_128, BLOCK_SIZE_256, DEFAULT_PAGE_SIZE,
 };