A few more small improvements to multiply

1 files changed, 60 insertions, 57 deletions

diff --git a/core/src/main/java/org/bouncycastle/math/ec/IntArray.java b/core/src/main/java/org/bouncycastle/math/ec/IntArray.java
index 7f1158f1..294f1e46 100644
--- a/core/src/main/java/org/bouncycastle/math/ec/IntArray.java
+++ b/core/src/main/java/org/bouncycastle/math/ec/IntArray.java
@@ -6,25 +6,29 @@ import java.math.BigInteger;
 
 class IntArray
 {
-    private static final int[] generateSquare8Table()
-    {
-        int[] t = new int[256];
-        for (int i = 0; i < 256; ++i)
-        {
-            int v = 0;
-            for (int bit = 0; bit < 8; ++bit)
-            {
-                if ((i & (1 << bit)) != 0)
-                {
-                    v ^= i << bit;
-                }
-            }
-            t[i] =  v << 16;
-        }
-        return t;
-    }
-
-    private static final int[] SQUARE8_TABLE = generateSquare8Table();
+    /*
+     * This expands 8 bit indices into 16 bit contents, by inserting 0s between bits.
+     * In a binary field, this operation is the same as squaring an 8 bit number.
+     */
+    private static final int[] EXPANSION_TABLE = new int[] { 0x0000, 0x0001, 0x0004, 0x0005, 0x0010, 0x0011, 0x0014,
+        0x0015, 0x0040, 0x0041, 0x0044, 0x0045, 0x0050, 0x0051, 0x0054, 0x0055, 0x0100, 0x0101, 0x0104, 0x0105, 0x0110,
+        0x0111, 0x0114, 0x0115, 0x0140, 0x0141, 0x0144, 0x0145, 0x0150, 0x0151, 0x0154, 0x0155, 0x0400, 0x0401, 0x0404,
+        0x0405, 0x0410, 0x0411, 0x0414, 0x0415, 0x0440, 0x0441, 0x0444, 0x0445, 0x0450, 0x0451, 0x0454, 0x0455, 0x0500,
+        0x0501, 0x0504, 0x0505, 0x0510, 0x0511, 0x0514, 0x0515, 0x0540, 0x0541, 0x0544, 0x0545, 0x0550, 0x0551, 0x0554,
+        0x0555, 0x1000, 0x1001, 0x1004, 0x1005, 0x1010, 0x1011, 0x1014, 0x1015, 0x1040, 0x1041, 0x1044, 0x1045, 0x1050,
+        0x1051, 0x1054, 0x1055, 0x1100, 0x1101, 0x1104, 0x1105, 0x1110, 0x1111, 0x1114, 0x1115, 0x1140, 0x1141, 0x1144,
+        0x1145, 0x1150, 0x1151, 0x1154, 0x1155, 0x1400, 0x1401, 0x1404, 0x1405, 0x1410, 0x1411, 0x1414, 0x1415, 0x1440,
+        0x1441, 0x1444, 0x1445, 0x1450, 0x1451, 0x1454, 0x1455, 0x1500, 0x1501, 0x1504, 0x1505, 0x1510, 0x1511, 0x1514,
+        0x1515, 0x1540, 0x1541, 0x1544, 0x1545, 0x1550, 0x1551, 0x1554, 0x1555, 0x4000, 0x4001, 0x4004, 0x4005, 0x4010,
+        0x4011, 0x4014, 0x4015, 0x4040, 0x4041, 0x4044, 0x4045, 0x4050, 0x4051, 0x4054, 0x4055, 0x4100, 0x4101, 0x4104,
+        0x4105, 0x4110, 0x4111, 0x4114, 0x4115, 0x4140, 0x4141, 0x4144, 0x4145, 0x4150, 0x4151, 0x4154, 0x4155, 0x4400,
+        0x4401, 0x4404, 0x4405, 0x4410, 0x4411, 0x4414, 0x4415, 0x4440, 0x4441, 0x4444, 0x4445, 0x4450, 0x4451, 0x4454,
+        0x4455, 0x4500, 0x4501, 0x4504, 0x4505, 0x4510, 0x4511, 0x4514, 0x4515, 0x4540, 0x4541, 0x4544, 0x4545, 0x4550,
+        0x4551, 0x4554, 0x4555, 0x5000, 0x5001, 0x5004, 0x5005, 0x5010, 0x5011, 0x5014, 0x5015, 0x5040, 0x5041, 0x5044,
+        0x5045, 0x5050, 0x5051, 0x5054, 0x5055, 0x5100, 0x5101, 0x5104, 0x5105, 0x5110, 0x5111, 0x5114, 0x5115, 0x5140,
+        0x5141, 0x5144, 0x5145, 0x5150, 0x5151, 0x5154, 0x5155, 0x5400, 0x5401, 0x5404, 0x5405, 0x5410, 0x5411, 0x5414,
+        0x5415, 0x5440, 0x5441, 0x5444, 0x5445, 0x5450, 0x5451, 0x5454, 0x5455, 0x5500, 0x5501, 0x5504, 0x5505, 0x5510,
+        0x5511, 0x5514, 0x5515, 0x5540, 0x5541, 0x5544, 0x5545, 0x5550, 0x5551, 0x5554, 0x5555 };
 
     // For toString(); must have length 32
     private static final String ZEROES = "00000000000000000000000000000000";
@@ -274,23 +278,21 @@ class IntArray
         for (int i = 0; i < usedLen; ++i)
         {
             int next = m_ints[i];
-            m_ints[i] = (next << 1) | (prev >>> 31);
-            prev = next;
+            m_ints[i] = (next << 1) | prev;
+            prev = next >>> 31;
         }
     }
 
-    private int shiftLeftQuick()
+    private static int shiftLeftQuick(int[] x, int count)
     {
-        int len = m_ints.length;
-
         int prev = 0;
-        for (int i = 0; i < len; ++i)
+        for (int i = 0; i < count; ++i)
         {
-            int next = m_ints[i];
-            m_ints[i] = (next << 1) | (prev >>> 31);
-            prev = next;
+            int next = x[i];
+            x[i] = (next << 1) | prev;
+            prev = next >>> 31;
         }
-        return prev >>> 31;
+        return prev;
     }
 
     public IntArray shiftLeft(int n)
@@ -328,10 +330,9 @@ class IntArray
 
     public void addOneShifted(int shift)
     {
-        int newMinUsedLen = 1 + shift;
-        if (newMinUsedLen > m_ints.length)
+        if (shift >= m_ints.length)
         {
-            m_ints = resizedInts(newMinUsedLen);
+            m_ints = resizedInts(shift + 1);
         }
 
         m_ints[shift] ^= 1;
@@ -342,9 +343,6 @@ class IntArray
         int words = bits >>> 5;
         int shift = bits & 0x1F;
 
-//        IntArray vzShift = other.shiftLeft(shift);
-//        addShiftedByWords(vzShift, words);
-
         if (shift == 0)
         {
             addShiftedByWords(other, words);
@@ -367,10 +365,10 @@ class IntArray
         for (int i = 0; i < otherUsedLen; ++i)
         {
             int next = other.m_ints[i];
-            m_ints[i + words] ^= (next << shift) | (prev >>> shiftInv);
-            prev = next;
+            m_ints[i + words] ^= (next << shift) | prev;
+            prev = next >>> shiftInv;
         }
-        m_ints[otherUsedLen + words] ^= prev >>> shiftInv;
+        m_ints[otherUsedLen + words] ^= prev;
     }
 
     public void addShiftedByWords(IntArray other, int words)
@@ -393,12 +391,11 @@ class IntArray
         }
     }
 
-    private void addShiftedByWordsQuick(IntArray other, int words)
+    private void addShiftedByWordsQuick(int[] x, int xOff, int[] y, int count)
     {
-        int otherLen = other.m_ints.length;
-        for (int i = 0; i < otherLen; ++i)
+        for (int i = 0; i < count; ++i)
         {
-            m_ints[words + i] ^= other.m_ints[i];
+            x[xOff + i] ^= y[i];
         }
     }
 
@@ -413,7 +410,7 @@ class IntArray
         int n = bit >>> 5;
         if (n < len)
         {
-            int shift = bit & 31;
+            int shift = bit & 0x1F;
             if (shift == 0)
             {
                 m_ints[n] ^= word;
@@ -437,7 +434,7 @@ class IntArray
         {
             return 0;
         }
-        int shift = bit & 31;
+        int shift = bit & 0x1F;
         if (shift == 0)
         {
             return m_ints[n];
@@ -537,30 +534,36 @@ class IntArray
             return new IntArray(1);
         }
 
-        int mLen = (m + 31) >>> 5;
-        int t = Math.min(usedLen, mLen);
+        int otherUsedLen = other.getUsedLength();
+        if (otherUsedLen == 0)
+        {
+            return new IntArray(1);
+        }
 
-        IntArray b = new IntArray(other.resizedInts(other.getUsedLength() + 1));
-        IntArray c = new IntArray(t + b.getLength());
+        int[] a = m_ints;
+        int bLen = otherUsedLen + 1;
+        int[] b = other.resizedInts(bLen);
+        int[] c = new int[usedLen + otherUsedLen];
 
         int testBit = 1;
         for (;;)
         {
-            for (int j = 0; j < t; j++)
+            for (int j = 0; j < usedLen; ++j)
             {
-                if ((m_ints[j] & testBit) != 0)
+                // If the kth bit of a[j] is set...
+                if ((a[j] & testBit) != 0)
                 {
-                    // The kth bit of m_ints[j] is set
-                    c.addShiftedByWordsQuick(b, j);
+                    addShiftedByWordsQuick(c, j, b, bLen);
                 }
             }
             if ((testBit <<= 1) == 0)
             {
                 break;
             }
-            b.shiftLeftQuick();
+
+            shiftLeftQuick(b, bLen);
         }
-        return c;
+        return new IntArray(c);
     }
 
     // public IntArray multiplyLeftToRight(IntArray other, int m) {
@@ -612,7 +615,7 @@ class IntArray
         }
 
         // Instead of flipping the high bits in the loop, explicitly clear any partial word above m bits
-        int partial = m & 31;
+        int partial = m & 0x1F;
         if (partial != 0)
         {
             m_ints[mLen - 1] &= (1 << partial) - 1;
@@ -644,7 +647,7 @@ class IntArray
 
     private void reduceWordWise(int from, int m, int[] ks)
     {
-        int pos = m + ((from - m) & ~31);
+        int pos = m + ((from - m) & ~0x1F);
         for (int i = pos; i >= m; i -= 32)
         {
             int word = getWord(i);
@@ -680,7 +683,7 @@ class IntArray
 
     private static int square16(int n)
     {
-        return (SQUARE8_TABLE[n & 0xFF] >>> 16) | SQUARE8_TABLE[n >>> 8];
+        return EXPANSION_TABLE[n & 0xFF] | EXPANSION_TABLE[n >>> 8] << 16;
     }
 
     public boolean equals(Object o)