utils.hpp

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#pragma once
 
#include <cstdint>
#include <cstring>
#include <stdexcept>
 
namespace Utils {
  using Byte = std::uint8_t;
  using Buffer = Byte*;
 
  inline Byte hexCharToByte(char x) {
    if(x >= '0' && x <= '9') return x - '0';
    if(x >= 'A' && x <= 'F') return x - 'A' + 10;
    if(x >= 'a' && x <= 'f') return x - 'a' + 10;
    throw std::invalid_argument("Invalid argument");
  }
 
  inline char byteToHexChar(Byte x) {
    if(x <= 9) return x + '0';
    if(x >= 10 && x <= 15) return (x - 10) + 'a';
    throw std::invalid_argument("Invalid argument");
  }
 
  inline std::size_t hexStringToBuffer(const char *input, std::size_t inputLength, Buffer output, bool stripZeroes = false) {
    if(stripZeroes) {
      while(*input == '0') {
        ++input;
        --inputLength;
      }
    }
    if(inputLength == 0) return 0;
 
    std::size_t outputLength = (inputLength + 1) / 2;
 
    if(inputLength % 2 == 1) {
      *(output++) = hexCharToByte(*(input++));
      --inputLength;
    }
 
    while(inputLength > 0) {
      *(output++) = 16 * hexCharToByte(*input) + hexCharToByte(*(input + 1));
      input += 2;
      inputLength -= 2;
    }
 
    return outputLength;
  }
 
  inline std::size_t hexStringToBuffer(const char *input, Buffer output, bool stripZeroes = false) {
    return hexStringToBuffer(input, strlen(input), output, stripZeroes);
  }
 
  inline std::size_t bufferToHexString(Buffer input, std::size_t inputLength, char *output, bool nullTerminated = false) {
    if(inputLength == 0) return 0;
 
    Buffer inputEnd = input + inputLength;
    while(input != inputEnd) {
      *output = byteToHexChar((*input / 16) % 16);
      *(output + 1) = byteToHexChar(*input % 16);
 
      ++input;
      output += 2;
    }
 
    if(nullTerminated) *output = '\0';
    
    return inputLength * 2;
  }
 
  inline std::size_t intToBuffer(std::uint64_t x, Buffer output) {
    std::size_t length = 0;
    if(x > 0xFFFFFFFFFFFFFF) length = 8;
    else if(x > 0xFFFFFFFFFFFF) length = 7;
    else if(x > 0xFFFFFFFFFF) length = 6;
    else if(x > 0xFFFFFFFF) length = 5;
    else if(x > 0xFFFFFF) length = 4;
    else if(x > 0xFFFF) length = 3;
    else if(x > 0xFF) length = 2;
    else if(x > 0) length = 1;
    else {
      *output = 0;
      return 1;
    }
 
    Buffer outputStart = output + length;
    for(; x != 0; x >>= 8) *(--outputStart) = x & 0xFF;
    return length;
  }
}