itoa.cpp

/*
itoa.cpp

Copyright (c) 23 Yann BOUCHER (yann)

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.

*/


#include <itoa.h>

#define MAX_PRECISION	(10)
static const double rounders[MAX_PRECISION + 1] =
{
    0.5,				// 0
    0.05,				// 1
    0.005,				// 2
    0.0005,				// 3
    0.00005,			// 4
    0.000005,			// 5
    0.0000005,			// 6
    0.00000005,			// 7
    0.000000005,		// 8
    0.0000000005,		// 9
    0.00000000005		// 10
};

char * ftoa(double f, char * buf, int precision)
{
    char * ptr = buf;
    char * p = ptr;
    char * p1;
    char c;
    long intPart;

    // check precision bounds
    if (precision > MAX_PRECISION)
        precision = MAX_PRECISION;

    // sign stuff
    if (f < 0)
    {
        f = -f;
        *ptr++ = '-';
    }

    if (precision < 0)  // negative precision == automatic precision guess
    {
        if (f < 1.0) precision = 6;
        else if (f < 10.0) precision = 5;
        else if (f < 100.0) precision = 4;
        else if (f < 1000.0) precision = 3;
        else if (f < 10000.0) precision = 2;
        else if (f < 100000.0) precision = 1;
        else precision = 0;
    }

    // round value according the precision
    if (precision)
        f += rounders[precision];

    // integer part...
    intPart = f;
    f -= intPart;

    if (!intPart)
        *ptr++ = '0';
    else
    {
        // save start pointer
        p = ptr;

        // convert (reverse order)
        while (intPart)
        {
            *p++ = '0' + intPart % 10;
            intPart /= 10;
        }

        // save end pos
        p1 = p;

        // reverse result
        while (p > ptr)
        {
            c = *--p;
            *p = *ptr;
            *ptr++ = c;
        }

        // restore end pos
        ptr = p1;
    }

    // decimal part
    if (precision)
    {
        // place decimal point
        *ptr++ = '.';

        // convert
        while (precision--)
        {
            f *= 10.0;
            c = f;
            *ptr++ = '0' + c;
            f -= c;
        }
    }

    // terminating zero
    *ptr = '\0';

    return buf;
}

int64_t itoa(int64_t value, char *sp, int radix)
{
    char tmp[65];// be careful with the length of the buffer
    char *tp = tmp;
    int64_t i;
    uint64_t v;

    int64_t sign = (radix == 10 && value < 0);
    if (sign)
        v = -value;
    else
        v = static_cast<uint64_t>(value);

    while (v || tp == tmp)
    {
        i = v % radix;
        v /= radix; // v/=radix uses less CPU clocks than v=v/radix does
        if (i < 10)
          *tp++ = i+'0';
        else
          *tp++ = i + 'a' - 10;
    }

    int64_t len = tp - tmp;

    if (sign)
    {
        *sp++ = '-';
        len++;
    }

    while (tp > tmp)
        *sp++ = *--tp;

    return len;
}