neobytes/src/script/compressor.cpp

// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2014 The Bitcoin developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include "compressor.h"

bool CScriptCompressor::IsToKeyID(CKeyID &hash) const
{
    if (script.size() == 25 && script[0] == OP_DUP && script[1] == OP_HASH160
                            && script[2] == 20 && script[23] == OP_EQUALVERIFY
                            && script[24] == OP_CHECKSIG) {
        memcpy(&hash, &script[3], 20);
        return true;
    }
    return false;
}

bool CScriptCompressor::IsToScriptID(CScriptID &hash) const
{
    if (script.size() == 23 && script[0] == OP_HASH160 && script[1] == 20
                            && script[22] == OP_EQUAL) {
        memcpy(&hash, &script[2], 20);
        return true;
    }
    return false;
}

bool CScriptCompressor::IsToPubKey(CPubKey &pubkey) const
{
    if (script.size() == 35 && script[0] == 33 && script[34] == OP_CHECKSIG
                            && (script[1] == 0x02 || script[1] == 0x03)) {
        pubkey.Set(&script[1], &script[34]);
        return true;
    }
    if (script.size() == 67 && script[0] == 65 && script[66] == OP_CHECKSIG
                            && script[1] == 0x04) {
        pubkey.Set(&script[1], &script[66]);
        return pubkey.IsFullyValid(); // if not fully valid, a case that would not be compressible
    }
    return false;
}

bool CScriptCompressor::Compress(std::vector<unsigned char> &out) const
{
    CKeyID keyID;
    if (IsToKeyID(keyID)) {
        out.resize(21);
        out[0] = 0x00;
        memcpy(&out[1], &keyID, 20);
        return true;
    }
    CScriptID scriptID;
    if (IsToScriptID(scriptID)) {
        out.resize(21);
        out[0] = 0x01;
        memcpy(&out[1], &scriptID, 20);
        return true;
    }
    CPubKey pubkey;
    if (IsToPubKey(pubkey)) {
        out.resize(33);
        memcpy(&out[1], &pubkey[1], 32);
        if (pubkey[0] == 0x02 || pubkey[0] == 0x03) {
            out[0] = pubkey[0];
            return true;
        } else if (pubkey[0] == 0x04) {
            out[0] = 0x04 | (pubkey[64] & 0x01);
            return true;
        }
    }
    return false;
}

unsigned int CScriptCompressor::GetSpecialSize(unsigned int nSize) const
{
    if (nSize == 0 || nSize == 1)
        return 20;
    if (nSize == 2 || nSize == 3 || nSize == 4 || nSize == 5)
        return 32;
    return 0;
}

bool CScriptCompressor::Decompress(unsigned int nSize, const std::vector<unsigned char> &in)
{
    switch(nSize) {
    case 0x00:
        script.resize(25);
        script[0] = OP_DUP;
        script[1] = OP_HASH160;
        script[2] = 20;
        memcpy(&script[3], &in[0], 20);
        script[23] = OP_EQUALVERIFY;
        script[24] = OP_CHECKSIG;
        return true;
    case 0x01:
        script.resize(23);
        script[0] = OP_HASH160;
        script[1] = 20;
        memcpy(&script[2], &in[0], 20);
        script[22] = OP_EQUAL;
        return true;
    case 0x02:
    case 0x03:
        script.resize(35);
        script[0] = 33;
        script[1] = nSize;
        memcpy(&script[2], &in[0], 32);
        script[34] = OP_CHECKSIG;
        return true;
    case 0x04:
    case 0x05:
        unsigned char vch[33] = {};
        vch[0] = nSize - 2;
        memcpy(&vch[1], &in[0], 32);
        CPubKey pubkey(&vch[0], &vch[33]);
        if (!pubkey.Decompress())
            return false;
        assert(pubkey.size() == 65);
        script.resize(67);
        script[0] = 65;
        memcpy(&script[1], pubkey.begin(), 65);
        script[66] = OP_CHECKSIG;
        return true;
    }
    return false;
}