adler32.cpp

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// 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, 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