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adler32.cpp

// adler32.cpp - 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, unsigned int length)
{
        const unsigned long BASE = 65521;

        unsigned long s1 = m_s1;
        unsigned long s2 = m_s2;

        while (length % 8 != 0)
        {
                s1 += *input++;
                s2 += s1;
                length--;
        }

        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;
        }

        m_s1 = (word16)s1;
        m_s2 = (word16)s2;
}

void Adler32::Final(byte *hash)
{
        hash[0] = byte(m_s2 >> 8);
        hash[1] = byte(m_s2);
        hash[2] = byte(m_s1 >> 8);
        hash[3] = byte(m_s1);

        Reset();
}

NAMESPACE_END

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