Minor refactoring

benchmarks/src/jvmMain/kotlin/space/kscience/kmath/benchmarks/BufferBenchmark.kt

@@ -15,11 +15,24 @@ import space.kscience.kmath.complex.complex
 import space.kscience.kmath.operations.invoke
 import space.kscience.kmath.structures.Buffer
 import space.kscience.kmath.structures.DoubleBuffer
+import space.kscience.kmath.structures.getDouble
+import space.kscience.kmath.structures.permute
 
 @State(Scope.Benchmark)
 internal class BufferBenchmark {
+
     @Benchmark
-    fun genericDoubleBufferReadWrite(blackhole: Blackhole) {
+    fun doubleArrayReadWrite(blackhole: Blackhole) {
+        val buffer = DoubleArray(size) { it.toDouble() }
+        var res = 0.0
+        (0 until size).forEach {
+            res += buffer[it]
+        }
+        blackhole.consume(res)
+    }
+
+    @Benchmark
+    fun doubleBufferReadWrite(blackhole: Blackhole) {
         val buffer = DoubleBuffer(size) { it.toDouble() }
         var res = 0.0
         (0 until size).forEach {
@@ -28,6 +41,26 @@ internal class BufferBenchmark {
         blackhole.consume(res)
     }
 
+    @Benchmark
+    fun bufferViewReadWrite(blackhole: Blackhole) {
+        val buffer = DoubleBuffer(size) { it.toDouble() }.permute(reversedIndices)
+        var res = 0.0
+        (0 until size).forEach {
+            res += buffer[it]
+        }
+        blackhole.consume(res)
+    }
+
+    @Benchmark
+    fun bufferViewReadWriteSpecialized(blackhole: Blackhole) {
+        val buffer = DoubleBuffer(size) { it.toDouble() }.permute(reversedIndices)
+        var res = 0.0
+        (0 until size).forEach {
+            res += buffer.getDouble(it)
+        }
+        blackhole.consume(res)
+    }
+
     @Benchmark
     fun complexBufferReadWrite(blackhole: Blackhole) = ComplexField {
         val buffer = Buffer.complex(size / 2) { Complex(it.toDouble(), -it.toDouble()) }
@@ -42,5 +75,6 @@ internal class BufferBenchmark {
 
     private companion object {
         private const val size = 100
+        private val reversedIndices = IntArray(size){it}.apply { reverse() }
     }
 }

examples/src/main/kotlin/space/kscience/kmath/series/analyzeDif.kt

@@ -5,6 +5,7 @@ import kotlinx.html.FlowContent
 import kotlinx.html.h1
 import space.kscience.kmath.operations.algebra
 import space.kscience.kmath.operations.bufferAlgebra
+import space.kscience.kmath.stat.ksComparisonStatistic
 import space.kscience.kmath.structures.Buffer
 import space.kscience.kmath.structures.slice
 import space.kscience.kmath.structures.toList
@@ -34,6 +35,8 @@ fun main() = with(Double.algebra.bufferAlgebra.seriesAlgebra()) {
     val s3: Buffer<Double> = s1.zip(s2) { l, r -> l + r } //s1 + s2
     val s4 = ln(s3)
 
+    val kmTest = ksComparisonStatistic(s1, s2)
+
     Plotly.page {
         h1 { +"This is my plot" }
         plotSeries(s1)

kmath-core/src/commonMain/kotlin/space/kscience/kmath/structures/BufferView.kt

@@ -79,11 +79,19 @@ public class BufferExpanded<T>(
 /**
  * Zero-copy select a slice inside the original buffer
  */
-public fun <T> Buffer<T>.slice(range: UIntRange): BufferView<T> = BufferSlice(
-    this,
-    range.first,
-    (range.last - range.first).toInt() + 1
-)
+public fun <T> Buffer<T>.slice(range: UIntRange): BufferView<T> = if (this is BufferSlice) {
+    BufferSlice(
+        origin,
+        this.offset + range.first,
+        (range.last - range.first).toInt() + 1
+    )
+} else {
+    BufferSlice(
+        this,
+        range.first,
+        (range.last - range.first).toInt() + 1
+    )
+}
 
 /**
  * Resize original buffer to a given range using given [range], filling additional segments with [defaultValue].

kmath-core/src/commonMain/kotlin/space/kscience/kmath/structures/bufferPrimitiveAccess.kt

@@ -5,7 +5,8 @@ import space.kscience.kmath.misc.UnstableKMathAPI
 /**
  * Non-boxing access to primitive [Double]
  */
-@OptIn(UnstableKMathAPI::class)
+
+@UnstableKMathAPI
 public fun Buffer<Double>.getDouble(index: Int): Double = if (this is BufferView) {
     val originIndex = originIndex(index)
     if( originIndex>=0) {
@@ -22,7 +23,7 @@ public fun Buffer<Double>.getDouble(index: Int): Double = if (this is BufferView
 /**
  * Non-boxing access to primitive [Int]
  */
-@OptIn(UnstableKMathAPI::class)
+@UnstableKMathAPI
 public fun Buffer<Int>.getInt(index: Int): Int = if (this is BufferView) {
     val originIndex = originIndex(index)
     if( originIndex>=0) {

kmath-stat/src/commonMain/kotlin/space/kscience/kmath/stat/StatisticalAlgebra.kt

@@ -1,5 +1,6 @@
 package space.kscience.kmath.stat
 
+import space.kscience.kmath.misc.UnstableKMathAPI
 import space.kscience.kmath.operations.*
 import space.kscience.kmath.structures.Buffer
 import space.kscience.kmath.structures.BufferFactory
@@ -20,12 +21,20 @@ public fun <T : Comparable<T>> StatisticalAlgebra<T, *, *>.ecdf(buffer: Buffer<T
 }
 
 /**
+ * Resulting value of kolmogorov-smirnov two-sample statistic
+ */
+@UnstableKMathAPI
+public data class KMComparisonResult<T : Comparable<T>>(val n: Int, val m: Int, val value: T)
+
+/**
+ * Kolmogorov-Smirnov sample comparison test
  * Implementation copied from https://commons.apache.org/proper/commons-math/javadocs/api-3.6.1/index.html?org/apache/commons/math3/stat/inference/KolmogorovSmirnovTest.html
  */
-public fun <T : Comparable<T>, A, BA : BufferAlgebra<T, A>> StatisticalAlgebra<T, A, BA>.kolmogorovSmirnovTest(
+@UnstableKMathAPI
+public fun <T : Comparable<T>, A, BA : BufferAlgebra<T, A>> StatisticalAlgebra<T, A, BA>.ksComparisonStatistic(
     x: Buffer<T>,
     y: Buffer<T>,
-): T where A : Group<T>, A : NumericAlgebra<T> = elementAlgebra.invoke {
+): KMComparisonResult<T> where A : Group<T>, A : NumericAlgebra<T> = elementAlgebra.invoke {
     // Copy and sort the sample arrays
     val sx = x.sorted()
     val sy = y.sorted()
@@ -41,19 +50,19 @@ public fun <T : Comparable<T>, A, BA : BufferAlgebra<T, A>> StatisticalAlgebra<T
     do {
         val z = if (sx[rankX] <= sy[rankY]) sx[rankX] else sy[rankY]
         while (rankX < n && sx[rankX].compareTo(z) == 0) {
-            rankX += 1;
-            curD += number(m);
+            rankX += 1
+            curD += number(m)
         }
 
         while (rankY < m && sy[rankY].compareTo(z) == 0) {
-            rankY += 1;
-            curD -= number(n);
+            rankY += 1
+            curD -= number(n)
         }
 
         when {
             curD > supD -> supD = curD
             -curD > supD -> supD = -curD
         }
-    } while (rankX < n && rankY < m);
-    return supD;
+    } while (rankX < n && rankY < m)
+    return KMComparisonResult(n, m, supD)
 }