1 files changed, 306 insertions, 0 deletions
diff --git a/libraries/spongycastle/core/src/main/java/org/spongycastle/pqc/math/linearalgebra/BigEndianConversions.java b/libraries/spongycastle/core/src/main/java/org/spongycastle/pqc/math/linearalgebra/BigEndianConversions.java
new file mode 100644
index 000000000..4ed7f1c91
--- /dev/null
+++ b/libraries/spongycastle/core/src/main/java/org/spongycastle/pqc/math/linearalgebra/BigEndianConversions.java
@@ -0,0 +1,306 @@
+package org.spongycastle.pqc.math.linearalgebra;
+
+
+/**
+ * This is a utility class containing data type conversions using big-endian
+ * byte order.
+ *
+ * @see LittleEndianConversions
+ */
+public final class BigEndianConversions
+{
+
+    /**
+     * Default constructor (private).
+     */
+    private BigEndianConversions()
+    {
+        // empty
+    }
+
+    /**
+     * Convert an integer to an octet string of length 4 according to IEEE 1363,
+     * Section 5.5.3.
+     *
+     * @param x the integer to convert
+     * @return the converted integer
+     */
+    public static byte[] I2OSP(int x)
+    {
+        byte[] result = new byte[4];
+        result[0] = (byte)(x >>> 24);
+        result[1] = (byte)(x >>> 16);
+        result[2] = (byte)(x >>> 8);
+        result[3] = (byte)x;
+        return result;
+    }
+
+    /**
+     * Convert an integer to an octet string according to IEEE 1363, Section
+     * 5.5.3. Length checking is performed.
+     *
+     * @param x    the integer to convert
+     * @param oLen the desired length of the octet string
+     * @return an octet string of length <tt>oLen</tt> representing the
+     *         integer <tt>x</tt>, or <tt>null</tt> if the integer is
+     *         negative
+     * @throws ArithmeticException if <tt>x</tt> can't be encoded into <tt>oLen</tt>
+     * octets.
+     */
+    public static byte[] I2OSP(int x, int oLen)
+        throws ArithmeticException
+    {
+        if (x < 0)
+        {
+            return null;
+        }
+        int octL = IntegerFunctions.ceilLog256(x);
+        if (octL > oLen)
+        {
+            throw new ArithmeticException(
+                "Cannot encode given integer into specified number of octets.");
+        }
+        byte[] result = new byte[oLen];
+        for (int i = oLen - 1; i >= oLen - octL; i--)
+        {
+            result[i] = (byte)(x >>> (8 * (oLen - 1 - i)));
+        }
+        return result;
+    }
+
+    /**
+     * Convert an integer to an octet string of length 4 according to IEEE 1363,
+     * Section 5.5.3.
+     *
+     * @param input  the integer to convert
+     * @param output byte array holding the output
+     * @param outOff offset in output array where the result is stored
+     */
+    public static void I2OSP(int input, byte[] output, int outOff)
+    {
+        output[outOff++] = (byte)(input >>> 24);
+        output[outOff++] = (byte)(input >>> 16);
+        output[outOff++] = (byte)(input >>> 8);
+        output[outOff] = (byte)input;
+    }
+
+    /**
+     * Convert an integer to an octet string of length 8 according to IEEE 1363,
+     * Section 5.5.3.
+     *
+     * @param input the integer to convert
+     * @return the converted integer
+     */
+    public static byte[] I2OSP(long input)
+    {
+        byte[] output = new byte[8];
+        output[0] = (byte)(input >>> 56);
+        output[1] = (byte)(input >>> 48);
+        output[2] = (byte)(input >>> 40);
+        output[3] = (byte)(input >>> 32);
+        output[4] = (byte)(input >>> 24);
+        output[5] = (byte)(input >>> 16);
+        output[6] = (byte)(input >>> 8);
+        output[7] = (byte)input;
+        return output;
+    }
+
+    /**
+     * Convert an integer to an octet string of length 8 according to IEEE 1363,
+     * Section 5.5.3.
+     *
+     * @param input  the integer to convert
+     * @param output byte array holding the output
+     * @param outOff offset in output array where the result is stored
+     */
+    public static void I2OSP(long input, byte[] output, int outOff)
+    {
+        output[outOff++] = (byte)(input >>> 56);
+        output[outOff++] = (byte)(input >>> 48);
+        output[outOff++] = (byte)(input >>> 40);
+        output[outOff++] = (byte)(input >>> 32);
+        output[outOff++] = (byte)(input >>> 24);
+        output[outOff++] = (byte)(input >>> 16);
+        output[outOff++] = (byte)(input >>> 8);
+        output[outOff] = (byte)input;
+    }
+
+    /**
+     * Convert an integer to an octet string of the specified length according
+     * to IEEE 1363, Section 5.5.3. No length checking is performed (i.e., if
+     * the integer cannot be encoded into <tt>length</tt> octets, it is
+     * truncated).
+     *
+     * @param input  the integer to convert
+     * @param output byte array holding the output
+     * @param outOff offset in output array where the result is stored
+     * @param length the length of the encoding
+     */
+    public static void I2OSP(int input, byte[] output, int outOff, int length)
+    {
+        for (int i = length - 1; i >= 0; i--)
+        {
+            output[outOff + i] = (byte)(input >>> (8 * (length - 1 - i)));
+        }
+    }
+
+    /**
+     * Convert an octet string to an integer according to IEEE 1363, Section
+     * 5.5.3.
+     *
+     * @param input the byte array holding the octet string
+     * @return an integer representing the octet string <tt>input</tt>, or
+     *         <tt>0</tt> if the represented integer is negative or too large
+     *         or the byte array is empty
+     * @throws ArithmeticException if the length of the given octet string is larger than 4.
+     */
+    public static int OS2IP(byte[] input)
+    {
+        if (input.length > 4)
+        {
+            throw new ArithmeticException("invalid input length");
+        }
+        if (input.length == 0)
+        {
+            return 0;
+        }
+        int result = 0;
+        for (int j = 0; j < input.length; j++)
+        {
+            result |= (input[j] & 0xff) << (8 * (input.length - 1 - j));
+        }
+        return result;
+    }
+
+    /**
+     * Convert a byte array of length 4 beginning at <tt>offset</tt> into an
+     * integer.
+     *
+     * @param input the byte array
+     * @param inOff the offset into the byte array
+     * @return the resulting integer
+     */
+    public static int OS2IP(byte[] input, int inOff)
+    {
+        int result = (input[inOff++] & 0xff) << 24;
+        result |= (input[inOff++] & 0xff) << 16;
+        result |= (input[inOff++] & 0xff) << 8;
+        result |= input[inOff] & 0xff;
+        return result;
+    }
+
+    /**
+     * Convert an octet string to an integer according to IEEE 1363, Section
+     * 5.5.3.
+     *
+     * @param input the byte array holding the octet string
+     * @param inOff the offset in the input byte array where the octet string
+     *              starts
+     * @param inLen the length of the encoded integer
+     * @return an integer representing the octet string <tt>bytes</tt>, or
+     *         <tt>0</tt> if the represented integer is negative or too large
+     *         or the byte array is empty
+     */
+    public static int OS2IP(byte[] input, int inOff, int inLen)
+    {
+        if ((input.length == 0) || input.length < inOff + inLen - 1)
+        {
+            return 0;
+        }
+        int result = 0;
+        for (int j = 0; j < inLen; j++)
+        {
+            result |= (input[inOff + j] & 0xff) << (8 * (inLen - j - 1));
+        }
+        return result;
+    }
+
+    /**
+     * Convert a byte array of length 8 beginning at <tt>inOff</tt> into a
+     * long integer.
+     *
+     * @param input the byte array
+     * @param inOff the offset into the byte array
+     * @return the resulting long integer
+     */
+    public static long OS2LIP(byte[] input, int inOff)
+    {
+        long result = ((long)input[inOff++] & 0xff) << 56;
+        result |= ((long)input[inOff++] & 0xff) << 48;
+        result |= ((long)input[inOff++] & 0xff) << 40;
+        result |= ((long)input[inOff++] & 0xff) << 32;
+        result |= ((long)input[inOff++] & 0xff) << 24;
+        result |= (input[inOff++] & 0xff) << 16;
+        result |= (input[inOff++] & 0xff) << 8;
+        result |= input[inOff] & 0xff;
+        return result;
+    }
+
+    /**
+     * Convert an int array into a byte array.
+     *
+     * @param input the int array
+     * @return the converted array
+     */
+    public static byte[] toByteArray(final int[] input)
+    {
+        byte[] result = new byte[input.length << 2];
+        for (int i = 0; i < input.length; i++)
+        {
+            I2OSP(input[i], result, i << 2);
+        }
+        return result;
+    }
+
+    /**
+     * Convert an int array into a byte array of the specified length. No length
+     * checking is performed (i.e., if the last integer cannot be encoded into
+     * <tt>length % 4</tt> octets, it is truncated).
+     *
+     * @param input  the int array
+     * @param length the length of the converted array
+     * @return the converted array
+     */
+    public static byte[] toByteArray(final int[] input, int length)
+    {
+        final int intLen = input.length;
+        byte[] result = new byte[length];
+        int index = 0;
+        for (int i = 0; i <= intLen - 2; i++, index += 4)
+        {
+            I2OSP(input[i], result, index);
+        }
+        I2OSP(input[intLen - 1], result, index, length - index);
+        return result;
+    }
+
+    /**
+     * Convert a byte array into an int array.
+     *
+     * @param input the byte array
+     * @return the converted array
+     */
+    public static int[] toIntArray(byte[] input)
+    {
+        final int intLen = (input.length + 3) / 4;
+        final int lastLen = input.length & 0x03;
+        int[] result = new int[intLen];
+
+        int index = 0;
+        for (int i = 0; i <= intLen - 2; i++, index += 4)
+        {
+            result[i] = OS2IP(input, index);
+        }
+        if (lastLen != 0)
+        {
+            result[intLen - 1] = OS2IP(input, index, lastLen);
+        }
+        else
+        {
+            result[intLen - 1] = OS2IP(input, index);
+        }
+
+        return result;
+    }
+
+}