Use faster fold + reduce_with in helpers

From benchmarks it increases performance by around 10% for cpa and
by 30-60% for snr.

src/cpa.rs

@@ -25,25 +25,24 @@ where
     assert_eq!(leakages.shape()[0], plaintexts.shape()[0]);
     assert!(chunk_size > 0);
 
+    // From benchmarks fold + reduce_with is faster than map + reduce/reduce_with and fold + reduce
     zip(
         leakages.axis_chunks_iter(Axis(0), chunk_size),
         plaintexts.axis_chunks_iter(Axis(0), chunk_size),
     )
     .par_bridge()
-    .map(|(leakages_chunk, plaintexts_chunk)| {
-        let mut cpa =
-            CpaProcessor::new(leakages.shape()[1], guess_range, target_byte, leakage_func);
-
-        for i in 0..leakages_chunk.shape()[0] {
-            cpa.update(leakages_chunk.row(i), plaintexts_chunk.row(i));
-        }
-
-        cpa
-    })
-    .reduce(
+    .fold(
         || CpaProcessor::new(leakages.shape()[1], guess_range, target_byte, leakage_func),
-        |a, b| a + b,
+        |mut cpa, (leakages_chunk, plaintexts_chunk)| {
+            for i in 0..leakages_chunk.shape()[0] {
+                cpa.update(leakages_chunk.row(i), plaintexts_chunk.row(i));
+            }
+
+            cpa
+        },
     )
+    .reduce_with(|a, b| a + b)
+    .unwrap()
     .finalize()
 }
 

src/cpa_normal.rs

@@ -28,15 +28,16 @@ where
         plaintexts.axis_chunks_iter(Axis(0), chunk_size),
     )
     .par_bridge()
-    .map(|(leakages_chunk, plaintexts_chunk)| {
-        let mut cpa = CpaProcessor::new(leakages.shape()[1], chunk_size, guess_range, leakage_func);
-        cpa.update(leakages_chunk, plaintexts_chunk);
-        cpa
-    })
-    .reduce(
+    .fold(
         || CpaProcessor::new(leakages.shape()[1], chunk_size, guess_range, leakage_func),
-        |x, y| x + y,
+        |mut cpa, (leakages_chunk, plaintexts_chunk)| {
+            cpa.update(leakages_chunk, plaintexts_chunk);
+
+            cpa
+        },
     )
+    .reduce_with(|x, y| x + y)
+    .unwrap()
     .finalize()
 }
 

src/dpa.rs

@@ -4,6 +4,8 @@ use std::{iter::zip, ops::Add};
 
 use crate::util::max_per_row;
 
+/// # Panics
+/// Panics if `chunk_size` is not strictly positive.
 pub fn dpa<M, T>(
     leakages: ArrayView2<T>,
     metadata: ArrayView1<M>,
@@ -15,24 +17,25 @@ where
     T: Into<f32> + Copy + Sync,
     M: Clone + Sync,
 {
+    assert!(chunk_size > 0);
+
     zip(
         leakages.axis_chunks_iter(Axis(0), chunk_size),
         metadata.axis_chunks_iter(Axis(0), chunk_size),
     )
     .par_bridge()
-    .map(|(leakages_chunk, metadata_chunk)| {
-        let mut dpa = DpaProcessor::new(leakages.shape()[1], guess_range, leakage_func);
-
-        for i in 0..leakages_chunk.shape()[0] {
-            dpa.update(leakages_chunk.row(i), metadata_chunk[i].clone());
-        }
-
-        dpa
-    })
-    .reduce(
+    .fold(
         || DpaProcessor::new(leakages.shape()[1], guess_range, leakage_func),
-        |a, b| a + b,
+        |mut dpa, (leakages_chunk, metadata_chunk)| {
+            for i in 0..leakages_chunk.shape()[0] {
+                dpa.update(leakages_chunk.row(i), metadata_chunk[i].clone());
+            }
+
+            dpa
+        },
     )
+    .reduce_with(|a, b| a + b)
+    .unwrap()
     .finalize()
 }
 

src/processors.rs

@@ -97,20 +97,22 @@ where
 {
     assert!(chunk_size > 0);
 
+    // From benchmarks fold + reduce_with is faster than map + reduce/reduce_with and fold + reduce
     leakages
         .axis_chunks_iter(Axis(0), chunk_size)
         .enumerate()
         .par_bridge()
-        .map(|(chunk_idx, leakages_chunk)| {
-            let mut snr = Snr::new(leakages.shape()[1], classes);
-
-            for i in 0..leakages_chunk.shape()[0] {
-                snr.process(leakages_chunk.row(i), get_class(chunk_idx + i));
-            }
-
-            snr
-        })
-        .reduce(|| Snr::new(leakages.shape()[1], classes), |a, b| a + b)
+        .fold(
+            || Snr::new(leakages.shape()[1], classes),
+            |mut snr, (chunk_idx, leakages_chunk)| {
+                for i in 0..leakages_chunk.shape()[0] {
+                    snr.process(leakages_chunk.row(i), get_class(chunk_idx + i));
+                }
+                snr
+            },
+        )
+        .reduce_with(|a, b| a + b)
+        .unwrap()
         .snr()
 }
 
@@ -169,14 +171,14 @@ impl Snr {
 
             let class_sum = self.classes_sum.slice(s![class, ..]);
             for i in 0..size {
-                acc[i] += (class_sum[i] as f64).powf(2.0) / (self.classes_count[class] as f64);
+                acc[i] += (class_sum[i] as f64).powi(2) / (self.classes_count[class] as f64);
             }
         }
 
         let var = self.mean_var.var();
         let mean = self.mean_var.mean();
         // V[E[L|X]]
-        let velx = (acc / self.mean_var.count as f64) - mean.mapv(|x| x.powf(2.0));
+        let velx = (acc / self.mean_var.count as f64) - mean.mapv(|x| x.powi(2));
         1f64 / (var / velx - 1f64)
     }
 }