JDK 8 core review request for 6989067 BigInteger's array copiers should be converted to System.arraycopy()

[joe.darcy at oracle.com]

Hello.

Please review this simple patch to replace explicit array copy loops 
with System.arraycopy:

    6989067 BigInteger's array copiers should be converted to 
System.arraycopy()
    http://cr.openjdk.java.net/~darcy/6989067.0/

Patch below.

Thanks,

-Joe

--- old/src/share/classes/java/math/BigInteger.java    2011-09-02 
14:48:34.000000000 -0700
+++ new/src/share/classes/java/math/BigInteger.java    2011-09-02 
14:48:34.000000000 -0700
@@ -1612,14 +1612,12 @@
         } else { // Array must be resized
             if (nBits <= (32-bitsInHighWord)) {
                 int result[] = new int[nInts+len];
-                for (int i=0; i<len; i++)
-                    result[i] = a[i];
+                System.arraycopy(a, 0, result, 0, len);
                 primitiveLeftShift(result, result.length, nBits);
                 return result;
             } else {
                 int result[] = new int[nInts+len+1];
-                for (int i=0; i<len; i++)
-                    result[i] = a[i];
+                System.arraycopy(a, 0, result, 0, len);
                 primitiveRightShift(result, result.length, 32 - nBits);
                 return result;
             }
@@ -1908,8 +1906,7 @@
 
         // Set t to high half of b
         int[] t = new int[modLen];
-        for(int i=0; i<modLen; i++)
-            t[i] = b[i];
+        System.arraycopy(b, 0, t, 0, modLen);
 
         // Fill in the table with odd powers of the base
         for (int i=1; i<tblmask; i++) {
@@ -2006,14 +2003,12 @@
 
         // Convert result out of Montgomery form and return
         int[] t2 = new int[2*modLen];
-        for(int i=0; i<modLen; i++)
-            t2[i+modLen] = b[i];
+        System.arraycopy(b, 0, t2, modLen, modLen);
 
         b = montReduce(t2, mod, modLen, inv);
 
         t2 = new int[modLen];
-        for(int i=0; i<modLen; i++)
-            t2[i] = b[i];
+        System.arraycopy(b, 0, t2, 0, modLen);
 
         return new BigInteger(1, t2);
     }
@@ -2154,8 +2149,7 @@
         // Copy remaining ints of mag
         int numInts = (p + 31) >>> 5;
         int[] mag = new int[numInts];
-        for (int i=0; i<numInts; i++)
-            mag[i] = this.mag[i + (this.mag.length - numInts)];
+        System.arraycopy(this.mag, (this.mag.length - numInts), mag, 0, 
numInts);
 
         // Mask out any excess bits
         int excessBits = (numInts << 5) - p;
@@ -2221,7 +2215,7 @@
                 return shiftRight(-n);
             }
         }
-        int[] newMag = shiftLeft(mag,n);
+        int[] newMag = shiftLeft(mag, n);
 
         return new BigInteger(newMag, signum);
     }
@@ -2234,8 +2228,7 @@
 
         if (nBits == 0) {
             newMag = new int[magLen + nInts];
-            for (int i=0; i<magLen; i++)
-                newMag[i] = mag[i];
+            System.arraycopy(mag, 0, newMag, 0, magLen);
         } else {
             int i = 0;
             int nBits2 = 32 - nBits;
@@ -2289,8 +2282,7 @@
         if (nBits == 0) {
             int newMagLen = magLen - nInts;
             newMag = new int[newMagLen];
-            for (int i=0; i<newMagLen; i++)
-                newMag[i] = mag[i];
+            System.arraycopy(mag, 0, newMag, 0, newMagLen);
         } else {
             int i = 0;
             int highBits = mag[0] >>> nBits;
@@ -2561,7 +2553,7 @@
                  if (signum < 0) {
                      // Check if magnitude is a power of two
                      boolean pow2 = (Integer.bitCount(mag[0]) == 1);
-                     for(int i=1; i< len && pow2; i++)
+                     for (int i=1; i< len && pow2; i++)
                          pow2 = (mag[i] == 0);
 
                      n = (pow2 ? magBitLength -1 : magBitLength);