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