ftoa.c

/**
 *  stm32tpl --  STM32 C++ Template Peripheral Library
 *  Visit https://github.com/antongus/stm32tpl for new versions
 *
 *  Copyright (c) 2011-2020 Anton B. Gusev aka AHTOXA
 *
 *  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.
 *
 *
 *  file         : ftoa.c
 *  description  : convert double to string
 *
 */

#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;
}