adler32.cpp

// adler32.cpp - originally written and placed in the public domain by Wei Dai
 
#include "pch.h"
#include "adler32.h"
 
NAMESPACE_BEGIN(CryptoPP)
 
void Adler32::Update(const byte *input, size_t length)
{
        const unsigned long BASE = 65521;
 
        unsigned long s1 = m_s1;
        unsigned long s2 = m_s2;
 
        if (length % 8 != 0)
        {
                do
                {
                        s1 += *input++;
                        s2 += s1;
                        length--;
                } while (length % 8 != 0);
 
                if (s1 >= BASE)
                        s1 -= BASE;
                s2 %= BASE;
        }
 
        while (length > 0)
        {
                s1 += input[0]; s2 += s1;
                s1 += input[1]; s2 += s1;
                s1 += input[2]; s2 += s1;
                s1 += input[3]; s2 += s1;
                s1 += input[4]; s2 += s1;
                s1 += input[5]; s2 += s1;
                s1 += input[6]; s2 += s1;
                s1 += input[7]; s2 += s1;
 
                length -= 8;
                input += 8;
 
                if (s1 >= BASE)
                        s1 -= BASE;
                if (length % 0x8000 == 0)
                        s2 %= BASE;
        }
 
        CRYPTOPP_ASSERT(s1 < BASE);
        CRYPTOPP_ASSERT(s2 < BASE);
 
        m_s1 = (word16)s1;
        m_s2 = (word16)s2;
}
 
void Adler32::TruncatedFinal(byte *hash, size_t size)
{
        ThrowIfInvalidTruncatedSize(size);
 
        switch (size)
        {
        default:
                hash[3] = byte(m_s1);
                // fall through
        case 3:
                hash[2] = byte(m_s1 >> 8);
                // fall through
        case 2:
                hash[1] = byte(m_s2);
                // fall through
        case 1:
                hash[0] = byte(m_s2 >> 8);
                // fall through
        case 0:
                ;
                // fall through
        }
 
        Reset();
}
 
NAMESPACE_END