diff options
Diffstat (limited to 'crypto/src/bcpg/Crc24.cs')
| -rw-r--r-- | crypto/src/bcpg/Crc24.cs | 54 |
1 files changed, 44 insertions, 10 deletions
diff --git a/crypto/src/bcpg/Crc24.cs b/crypto/src/bcpg/Crc24.cs index 54c9f2f5a..66cea0b06 100644 --- a/crypto/src/bcpg/Crc24.cs +++ b/crypto/src/bcpg/Crc24.cs @@ -1,5 +1,3 @@ -using System; - namespace Org.BouncyCastle.Bcpg { public sealed class Crc24 @@ -7,6 +5,41 @@ namespace Org.BouncyCastle.Bcpg private const int Crc24Init = 0x0b704ce; private const int Crc24Poly = 0x1864cfb; + private static readonly int[] Table0, Table8, Table16; + + static Crc24() + { + int[] table0 = new int[256]; + int[] table8 = new int[256]; + int[] table16 = new int[256]; + + int crc = 0x800000; + for (int i = 1; i < 256; i <<= 1) + { + int carry = ((crc << 8) >> 31) & Crc24Poly; + crc = (crc << 1) ^ carry; + + for (int j = 0; j < i; ++j) + { + table0[i + j] = crc ^ table0[j]; + } + } + + for (int i = 1; i < 256; ++i) + { + int crc0 = table0[i]; + int crc8 = ((crc0 & 0xFFFF) << 8) ^ table0[(crc0 >> 16) & 255]; + int crc16 = ((crc8 & 0xFFFF) << 8) ^ table0[(crc8 >> 16) & 255]; + + table8[i] = crc8; + table16[i] = crc16; + } + + Table0 = table0; + Table8 = table8; + Table16 = table16; + } + private int m_crc = Crc24Init; public Crc24() @@ -15,17 +48,18 @@ namespace Org.BouncyCastle.Bcpg public void Update(byte b) { - m_crc ^= (int)b << 16; - for (int i = 0; i < 8; i++) - { - int carry = -((m_crc >> 23) & 1) & Crc24Poly; + int index = (b ^ (m_crc >> 16)) & 255; + m_crc = (m_crc << 8) ^ Table0[index]; + } - m_crc <<= 1; - m_crc ^= carry; - } + public void Update3(byte[] buf, int off) + { + m_crc = Table16[(buf[off + 0] ^ (m_crc >> 16)) & 255] + ^ Table8[(buf[off + 1] ^ (m_crc >> 8)) & 255] + ^ Table0[(buf[off + 2] ^ m_crc) & 255]; } - public int Value => m_crc; + public int Value => m_crc & 0xFFFFFF; public void Reset() { |