org.bouncycastle.bcpg.FastCRC24 Maven / Gradle / Ivy
package org.bouncycastle.bcpg;
public class FastCRC24
extends CRC24
{
private static final int[] TABLE = getTable();
/**
* Fast CRC-24 implementation using a lookup table to handle multiple bits at a time.
*
* Compare: Sarwate, Dilip V. "Computation of cyclic redundancy checks via table look-up."
*/
public FastCRC24()
{
}
public void update(int b)
{
// b^(crc>>16) mod 256
int index = (b ^ (crc >> 16)) & ~-256;
crc = (crc << 8) ^ TABLE[index];
}
/**
* Lazily init and return the lookup table.
*
* @return lookup table
*/
private static int[] getTable()
{
int[] TABLE = new int[256];
int crc = 0x800000;
int i = 1;
while (i != 256)
{
if ((crc & 0x800000) > 0)
{
crc = (crc << 1) ^ CRC24_POLY;
}
else
{
crc <<= 1;
}
for (int j = 0; j < i; j++)
{
TABLE[i + j] = crc ^ TABLE[j];
}
i <<= 1;
}
return TABLE;
}
}