Adler32.cpp

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#include <sourcepp/crypto/Adler32.h>
 
#include <BufferStream.h>
 
using namespace sourcepp;

namespace tomcrypt {
 
namespace {
 
struct adler32_state {
    uint16_t s[2];
};
 
constexpr uint32_t s_adler32_base = 65521;
 
[[nodiscard]] bool adler32_update(adler32_state& ctx, const uint8_t* input, uint64_t length) {
    if (!input) {
        return false;
    }
 
    uint64_t s1 = ctx.s[0];
    uint64_t s2 = ctx.s[1];
 
    if (length % 8 != 0) {
        do {
            s1 += *input++;
            s2 += s1;
            length--;
        } while (length % 8 != 0);
 
        if (s1 >= s_adler32_base) {
            s1 -= s_adler32_base;
        }
        s2 %= s_adler32_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 >= s_adler32_base) {
            s1 -= s_adler32_base;
        }
        s2 %= s_adler32_base;
    }
 
    if (s1 >= s_adler32_base || s2 >= s_adler32_base) {
        return false;
    }
 
    ctx.s[0] = static_cast<uint16_t>(s1);
    ctx.s[1] = static_cast<uint16_t>(s2);
    return true;
}
 
[[nodiscard]] uint32_t adler32_finish(const adler32_state& ctx) {
    return (static_cast<uint32_t>(ctx.s[1]) << 16) | (static_cast<uint32_t>(ctx.s[0]) << 0);
}
 
} // namespace
 
} // namespace tomcrypt
 
uint32_t crypto::computeAdler32(std::span<const std::byte> buffer) {
    if (buffer.empty()) {
        return 0;
    }
 
    // NOTE: tomcrypt adler32 initializes state to (1, 0). GCF needs (0, 0) so we are skipping the standard init
    tomcrypt::adler32_state adler32{};
    if (!tomcrypt::adler32_update(adler32, reinterpret_cast<const uint8_t*>(buffer.data()), buffer.size())) {
        return 0;
    }
    return tomcrypt::adler32_finish(adler32);
}