[GitHub] [commons-math] aherbert commented on a diff in pull request #219: MATH-1569 - Manual array copy.

[GitBox <gi...@apache.org>]

aherbert commented on code in PR #219:
URL: https://github.com/apache/commons-math/pull/219#discussion_r1001149401


##########
commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/analysis/function/Logit.java:
##########
@@ -182,9 +182,7 @@ public DerivativeStructure value(final DerivativeStructure t)
             //  for x close to hi the signs will always be +inf)
             // this is probably overkill, since the call to compose at the end
             // of the method will transform most infinities into NaN ...
-            for (int i = 2; i < f.length; ++i) {
-                f[i] = f[i - 2];
-            }
+            if (f.length - 2 >= 0) System.arraycopy(f, 0, f, 2, f.length - 2);

Review Comment:
   `> 0`



##########
commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/optim/nonlinear/scalar/noderiv/CMAESOptimizer.java:
##########
@@ -752,9 +752,7 @@ private void updateBD(double negccov) {
      * @param val Current best fitness value.
      */
     private static void push(double[] vals, double val) {
-        for (int i = vals.length-1; i > 0; i--) {
-            vals[i] = vals[i-1];
-        }
+        if (vals.length - 1 >= 0) System.arraycopy(vals, 0, vals, 1, vals.length - 1);

Review Comment:
   `> 0`



##########
commons-math-legacy-core/src/main/java/org/apache/commons/math4/legacy/core/dfp/Dfp.java:
##########
@@ -663,9 +663,7 @@ public Dfp getTwo() {
     /** Shift the mantissa left, and adjust the exponent to compensate.
      */
     protected void shiftLeft() {
-        for (int i = mant.length - 1; i > 0; i--) {
-            mant[i] = mant[i - 1];
-        }
+        if (mant.length - 1 >= 0) System.arraycopy(mant, 0, mant, 1, mant.length - 1);

Review Comment:
   use `> 0` as arraycopy with a length of 0 is a wasted call to a native method. Add enclosing braces to fix checkstyle.



##########
commons-math-legacy-core/src/main/java/org/apache/commons/math4/legacy/core/dfp/Dfp.java:
##########
@@ -675,9 +673,7 @@ uses shiftRight() */
     /** Shift the mantissa right, and adjust the exponent to compensate.
      */
     protected void shiftRight() {
-        for (int i = 0; i < mant.length - 1; i++) {
-            mant[i] = mant[i + 1];
-        }
+        if (mant.length - 1 >= 0) System.arraycopy(mant, 1, mant, 0, mant.length - 1);

Review Comment:
   `> 0`



##########
commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/ode/nonstiff/AdamsNordsieckFieldTransformer.java:
##########
@@ -170,10 +170,8 @@ private AdamsNordsieckFieldTransformer(final Field<T> field, final int n) {
         // Nordsieck to multistep, then shifting rows to represent step advance
         // then applying inverse transform
         T[][] shiftedP = bigP.getData();
-        for (int i = shiftedP.length - 1; i > 0; --i) {
-            // shift rows
-            shiftedP[i] = shiftedP[i - 1];
-        }
+        // shift rows
+        if (shiftedP.length - 1 >= 0) System.arraycopy(shiftedP, 0, shiftedP, 1, shiftedP.length - 1);

Review Comment:
   `> 0`



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