About convert int to char

[xiaguan]

wan ji zhuan shu ru fa le.

About convert int to char (in logstream):

muduo:

template<typename T>
size_t convert(char buf[], T value)
{
  T i = value;
  char* p = buf;

  do
  {
    int lsd = static_cast<int>(i % 10); 
    i /= 10;
    *p++ = zero[lsd];
  } while (i != 0);  // 

  if (value < 0)
  {
    *p++ = '-';
  }
  *p = '\0';
  std::reverse(buf, p);

  return p - buf;
}

i think some % and / is unncessary.They cause performence lose.
std perfomence betterat least on my machine :

std:

template<typename _Tp>
    void
    __to_chars_10_impl(char* __first, unsigned __len, _Tp __val) noexcept
    {
      static_assert(is_integral<_Tp>::value, "implementation bug");
      static_assert(is_unsigned<_Tp>::value, "implementation bug");

      static constexpr char __digits[201] =
	"0001020304050607080910111213141516171819"
	"2021222324252627282930313233343536373839"
	"4041424344454647484950515253545556575859"
	"6061626364656667686970717273747576777879"
	"8081828384858687888990919293949596979899";
      unsigned __pos = __len - 1;
      while (__val >= 100)
	{
	  auto const __num = (__val % 100) * 2;
	  __val /= 100;
	  __first[__pos] = __digits[__num + 1];
	  __first[__pos - 1] = __digits[__num];
	  __pos -= 2;
	}
      if (__val >= 10)
	{
	  auto const __num = __val * 2;
	  __first[1] = __digits[__num + 1];
	  __first[0] = __digits[__num];
	}
      else
	__first[0] = '0' + __val;
    }

} // namespace __detail

here 's test

#include <iostream>
#include <string>
#include <vector>

const int range_num = 1e6;

char buf[20];

#include <chrono>
class Timer{
public:
    explicit Timer(std::string  name ="Timer"):m_name(std::move(name)){}
    void start() noexcept {
        begin = std::chrono::high_resolution_clock::now();
    }
    void end(){
        auto end = std::chrono::high_resolution_clock::now();
        auto result = std::chrono::duration<double,std::ratio<1,1000>>(end-begin);
        std::cout <<m_name<<" live for "<<result.count() <<" ms"<<std::endl;
    }
private:
    std::string m_name;
    decltype(std::chrono::high_resolution_clock::now()) begin;
};
Timer timer;

static inline unsigned gcc_get_int_len(int val){
    static constexpr unsigned base = 10;
    static constexpr unsigned b2 = 100;
    static constexpr unsigned b3 = 1000;
    static constexpr unsigned  b4 = 10000;

    unsigned int n = 1;
    while(true){
        if(val < base ) return n;
        if(val < b2) return n+1;
        if(val < b3) return n+2;
        if(val < b4) return n+3;
        val /= b4;
        n += 4;
    }
}

static inline void gcc_test(int val){
    // if val is negative then isNeg  = 1; so we skip the firt byte to write
    const bool isNeg = val < 0;
    const unsigned unVal = isNeg ? (unsigned)~val + 1u : val;
    const auto valLen = gcc_get_int_len(unVal);

    static constexpr char __digits[201] =
            "0001020304050607080910111213141516171819"
            "2021222324252627282930313233343536373839"
            "4041424344454647484950515253545556575859"
            "6061626364656667686970717273747576777879"
            "8081828384858687888990919293949596979899";

    buf[isNeg] = '-';

    char * first = &buf[isNeg];

    // we need three param
    // char * first
    // int val
    // unsigned valLen (the len of the val)

    unsigned pos = valLen -1;

    while(val >= 100){
        auto const num = (val % 100) * 2;  // to find the idx in digits
        val /= 100;
        first[pos] = __digits[num + 1];
        first[pos - 1] = __digits[num];
        pos -= 2;
    }

    if(val >= 10){
        auto const num  = val * 2;
        first[1] = __digits[num+1];
        first[0] = __digits[num];
    }else{
        first[0] = '0' + val;
    }
}

const char digits[] = "9876543210123456789";
const char* zero = digits + 9;

static inline void muduo_test(int value)
{
    int i = value;
    char* p = buf;

    do
    {
        int lsd = static_cast<int>(i % 10);
        i /= 10;
        *p++ = zero[lsd];
    } while (i != 0);

    if (value < 0)
    {
        *p++ = '-';
    }
    *p = '\0';
    std::reverse(buf, p);
}

void for_test(){
    timer.start();
    for(int i = -range_num;i<=range_num;i++){
        for(int j = -1000;j<=1000;j++) muduo_test(j);
    }
    for(int i = -range_num * 10 ; i<=range_num * 10;i++){
        muduo_test(i);
    }
    timer.end();
    timer.start();
    for(int i = -range_num;i<=range_num;i++){
        for(int j = -1000;j<=1000;j++) gcc_test(j);
    }
    for(int i = -range_num * 10 ; i<=range_num * 10 ;i++){
        gcc_test(i);
    }
    timer.end();
}

int main() {
    for_test();
}

result(realease build):
Timer live for 20034.4 ms(muduo)
Timer live for 10197.1 ms(std)

un my laptop:
Timer live for 45365.2 ms
Timer live for 19382.4 ms