[sis] 02/02: Avoid the call to `Arrays.binarySearch(…)`. It has been identified by profiling as a performance bottleneck (in the context of `Isolines`).

[de...@apache.org]

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desruisseaux pushed a commit to branch geoapi-4.0
in repository https://gitbox.apache.org/repos/asf/sis.git

commit 11c6b74bf448ebc5c2e32fa2afca95f8f274798d
Author: Martin Desruisseaux <ma...@geomatys.com>
AuthorDate: Sat Dec 26 15:28:33 2020 +0100

    Avoid the call to `Arrays.binarySearch(…)`. It has been identified by profiling as a performance bottleneck (in the context of `Isolines`).
---
 .../internal/processing/image/IsolineTracer.java   |  2 +-
 .../sis/internal/processing/image/Isolines.java    | 23 ++++++----------------
 2 files changed, 7 insertions(+), 18 deletions(-)

diff --git a/core/sis-feature/src/main/java/org/apache/sis/internal/processing/image/IsolineTracer.java b/core/sis-feature/src/main/java/org/apache/sis/internal/processing/image/IsolineTracer.java
index 8f8f1c4..e42e362 100644
--- a/core/sis-feature/src/main/java/org/apache/sis/internal/processing/image/IsolineTracer.java
+++ b/core/sis-feature/src/main/java/org/apache/sis/internal/processing/image/IsolineTracer.java
@@ -103,7 +103,7 @@ final class IsolineTracer {
      */
     final class Level {
         /**
-         * The level value. This is a copy of {@link Isolines#levelValues} at the index of this level.
+         * The level value.
          *
          * @see #interpolate(int, int)
          */
diff --git a/core/sis-feature/src/main/java/org/apache/sis/internal/processing/image/Isolines.java b/core/sis-feature/src/main/java/org/apache/sis/internal/processing/image/Isolines.java
index 5f359e2..e1c6443 100644
--- a/core/sis-feature/src/main/java/org/apache/sis/internal/processing/image/Isolines.java
+++ b/core/sis-feature/src/main/java/org/apache/sis/internal/processing/image/Isolines.java
@@ -53,17 +53,7 @@ import static org.apache.sis.internal.processing.image.IsolineTracer.LOWER_RIGHT
  */
 public final class Isolines {
     /**
-     * Values for which to compute isolines, sorted in ascending order and without NaN values.
-     * This array is used for {@linkplain Arrays#binarySearch(double[], double) binary searches}.
-     * Each value is associated to an instance in the {@link #levels} array.
-     *
-     * @see IsolineTracer.Level#value
-     */
-    private final double[] levelValues;
-
-    /**
-     * Isoline data for each level.
-     * The length of this array is equal to the {@link #levelValues} array length.
+     * Isoline data for each level, sorted in ascending order of {@link IsolineTracer.Level#value}.
      */
     private final IsolineTracer.Level[] levels;
 
@@ -82,10 +72,9 @@ public final class Isolines {
                 System.arraycopy(values, i, values, i-1, n-- - i);
             }
         }
-        levelValues = ArraysExt.resize(values, n);
         levels = new IsolineTracer.Level[n];
         for (int i=0; i<n; i++) {
-            levels[i] = tracer.new Level(levelValues[i], width);
+            levels[i] = tracer.new Level(values[i], width);
         }
     }
 
@@ -112,10 +101,10 @@ public final class Isolines {
      *               {@value IsolineTracer#LOWER_LEFT} or {@value IsolineTracer#LOWER_RIGHT}.
      */
     private void setMaskBit(final DoubleBuffer data, final int bit) {
-        int i = Arrays.binarySearch(levelValues, data.get());
-        if (i < 0) i = ~i;          // Really tild, not minus.
-        while (--i >= 0) {          // Value is higher than all levels below `i`.
-            levels[i].isDataAbove |= bit;
+        final double value = data.get();
+        for (final IsolineTracer.Level level : levels) {
+            if (level.value > value) break;                 // See above javadoc for NaN handling.
+            level.isDataAbove |= bit;
         }
     }