spdlog/include/spdlog/details/fast_istostr.h

/*************************************************************************/
/* spdlog - an extremely fast and easy to use c++11 logging library.     */
/* Copyright (c) 2014 Gabi Melman.                                       */
/*                                                                       */
/* Permission is hereby granted, free of charge, to any person obtaining */
/* a copy of this software and associated documentation files (the       */
/* "Software"), to deal in the Software without restriction, including   */
/* without limitation the rights to use, copy, modify, merge, publish,   */
/* distribute, sublicense, and/or sell copies of the Software, and to    */
/* permit persons to whom the Software is furnished to do so, subject to */
/* the following conditions:                                             */
/*                                                                       */
/* The above copyright notice and this permission notice shall be        */
/* included in all copies or substantial portions of the Software.       */
/*                                                                       */
/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
/*************************************************************************/

#pragma once
#include <string>

//Fast to int to string
//Base on :http://stackoverflow.com/a/4351484/192001
//Modified version to pad zeros according to padding arg

namespace spdlog
{
namespace details
{

const char digit_pairs[201] =
{
    "00010203040506070809"
    "10111213141516171819"
    "20212223242526272829"
    "30313233343536373839"
    "40414243444546474849"
    "50515253545556575859"
    "60616263646566676869"
    "70717273747576777879"
    "80818283848586878889"
    "90919293949596979899"
};


inline std::string& fast_itostr(int n, std::string& s, size_t padding)
{
    if (n == 0)
    {
        s = std::string(padding, '0');
        return s;
    }

    int sign = -(n < 0);
    unsigned int val = static_cast<unsigned int>((n^sign) - sign);

    size_t size;
    if (val >= 10000)
    {
        if (val >= 10000000)
        {
            if (val >= 1000000000)
                size = 10;
            else if (val >= 100000000)
                size = 9;
            else
                size = 8;
        }
        else
        {
            if (val >= 1000000)
                size = 7;
            else if (val >= 100000)
                size = 6;
            else
                size = 5;
        }
    }
    else
    {
        if (val >= 100)
        {
            if (val >= 1000)
                size = 4;
            else
                size = 3;
        }
        else
        {
            if (val >= 10)
                size = 2;
            else
                size = 1;
        }
    }
    size -= sign;
    if (size < padding)
        size = padding;

    s.resize(size);
    char* c = &s[0];
    if (sign)
        *c = '-';

    c += size - 1;
    while (val >= 100)
    {
        size_t pos = val % 100;
        val /= 100;
        *(short*)(c - 1) = *(short*)(digit_pairs + 2 * pos);
        c -= 2;
    }
    while (val > 0)
    {
        *c-- = static_cast<char>('0' + (val % 10));
        val /= 10;
    }

    while (c >= s.data())
        *c-- = '0';
    return s;
}
}
}