little-endian-encode.cpp

#include <stdint.h>
#include <string>
#include <sstream>
#include <iomanip>
#include <iostream>
#include <vector>

inline uint16_t swap_endianness_16(uint16_t x)
{
    return (x >> 8) | (x << 8);
}

inline uint32_t swap_endianness_32(uint32_t x)
{
    return (((x & 0xff000000U) >> 24) | ((x & 0x00ff0000U) >>  8) |
    ((x & 0x0000ff00U) <<  8) | ((x & 0x000000ffU) << 24));
}

std::string ToHex(uint32_t value, int length)
{
    std::stringstream strBuffer;
    if (length == 2){
        strBuffer << std::hex << std::setw(length) << std::setfill('0') << value;
    } else if (length == 4){
        uint16_t be_value = (uint16_t)value;
        uint16_t le_value = swap_endianness_16(be_value);
        strBuffer << std::hex << std::setw(length) << std::setfill('0') << le_value;
    } else if (length == 8){
        uint32_t le_value = swap_endianness_32(value);
        strBuffer << std::hex << std::setw(length) << std::setfill('0') << le_value;
    }
    return strBuffer.str();
}

uint32_t FromChars(unsigned char a, unsigned char b)
{
    uint32_t n = b;
    n <<= 8;
    n += a;

    return n;
}

uint32_t FromChars(unsigned char a, unsigned char b, unsigned char c, unsigned char d)
{
    uint32_t n = d;
    n <<= 8;
    n += c;
    n <<= 8;
    n += b;
    n <<= 8;
    n += a;

    return n;
}

const signed char p_util_hexdigit[256] =
    {
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        0, 1, 2, 3, 4, 5, 6, 7, 8, 9, -1, -1, -1, -1, -1, -1,
        -1, 0xa, 0xb, 0xc, 0xd, 0xe, 0xf, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, 0xa, 0xb, 0xc, 0xd, 0xe, 0xf, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
};

signed char HexDigit(char c)
{
    return p_util_hexdigit[(unsigned char)c];
}

std::vector<unsigned char> ParseHex(const char* psz)
{
    // convert hex dump to vector
    std::vector<unsigned char> vch;
    while (true) {
        while (isspace(*psz))
            psz++;
        signed char c = HexDigit(*psz++);
        if (c == (signed char)-1)
            break;
        unsigned char n = (c << 4);
        c = HexDigit(*psz++);
        if (c == (signed char)-1)
            break;
        n |= c;
        vch.push_back(n);
    }
    return vch;
}

int main()
{
    // OP CODE produced from Python script.
    const char* vOpCode = "420105c10100005091000098530000e0920000";

    std::vector<unsigned char> v = ParseHex(vOpCode);
    std::string opCode(v.begin(), v.end());

    std::cout << FromChars(opCode[3], opCode[4], opCode[5], opCode[6]) << "\n";
    std::cout << FromChars(opCode[7], opCode[8], opCode[9], opCode[10]) << "\n";
    std::cout << FromChars(opCode[11], opCode[12], opCode[13], opCode[14]) << "\n";
    std::cout << FromChars(opCode[15], opCode[16], opCode[17], opCode[18]) << "\n";

    return 0;
}