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Gregory Nutt 2016-10-20 12:57:27 -06:00
parent 30ab01b1d8
commit 2b22666554
1 changed files with 252 additions and 0 deletions
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libc/stdlib/lib_strtof.c Normal file
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/****************************************************************************
* libc/stdlib/lib_strtof.c
* Convert string to float
*
* Copyright (C) 2016 Gregory Nutt. All rights reserved.
*
* A pretty straight forward conversion fo strtod():
*
* Copyright (C) 2002 Michael Ringgaard. All rights reserved.
* Copyright (C) 2006-2007 H. Peter Anvin.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the project nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <nuttx/compiler.h>
#include <stdlib.h>
#include <ctype.h>
#include <errno.h>
#ifdef CONFIG_HAVE_DOUBLE
/****************************************************************************
* Pre-processor definitions
****************************************************************************/
/* These are predefined with GCC, but could be issues for other compilers. If
* not defined, an arbitrary big number is put in for now. These should be
* added to nuttx/compiler for your compiler.
*/
#if !defined(__FLT_MIN_EXP__) || !defined(__FLT_MAX_EXP__)
# ifdef CONFIG_CPP_HAVE_WARNING
# warning "Size of exponent is unknown"
# endif
# undef __FLT_MIN_EXP__
# define __FLT_MIN_EXP__ (-125)
# undef __FLT_MAX_EXP__
# define __FLT_MAX_EXP__ (128)
#endif
/****************************************************************************
* Private Functions
****************************************************************************/
static inline int is_real(float x)
{
const float infinite = 1.0/0.0;
return (x < infinite) && (x >= -infinite);
}
/****************************************************************************
* Public Functions
****************************************************************************/
/***************************************************(************************
* Name: strtof
*
* Description:
* Convert a string to a float value
*
****************************************************************************/
float strtof(FAR const char *str, FAR char **endptr)
{
float number;
int exponent;
int negative;
FAR char *p = (FAR char *) str;
float p10;
int n;
int num_digits;
int num_decimals;
const float infinite = 1.0/0.0;
/* Skip leading whitespace */
while (isspace(*p))
{
p++;
}
/* Handle optional sign */
negative = 0;
switch (*p)
{
case '-':
negative = 1; /* Fall through to increment position */
case '+':
p++;
default:
break;
}
number = 0.;
exponent = 0;
num_digits = 0;
num_decimals = 0;
/* Process string of digits */
while (isdigit(*p))
{
number = number * 10. + (*p - '0');
p++;
num_digits++;
}
/* Process decimal part */
if (*p == '.')
{
p++;
while (isdigit(*p))
{
number = number * 10. + (*p - '0');
p++;
num_digits++;
num_decimals++;
}
exponent -= num_decimals;
}
if (num_digits == 0)
{
set_errno(ERANGE);
number = 0.0;
goto errout;
}
/* Correct for sign */
if (negative)
{
number = -number;
}
/* Process an exponent string */
if (*p == 'e' || *p == 'E')
{
/* Handle optional sign */
negative = 0;
switch (*++p)
{
case '-':
negative = 1; /* Fall through to increment pos */
case '+':
p++;
default:
break;
}
/* Process string of digits */
n = 0;
while (isdigit(*p))
{
n = n * 10 + (*p - '0');
p++;
}
if (negative)
{
exponent -= n;
}
else
{
exponent += n;
}
}
if (exponent < __FLT_MIN_EXP__ ||
exponent > __FLT_MAX_EXP__)
{
set_errno(ERANGE);
number = infinite;
goto errout;
}
/* Scale the result */
p10 = 10.;
n = exponent;
if (n < 0) n = -n;
while (n)
{
if (n & 1)
{
if (exponent < 0)
{
number /= p10;
}
else
{
number *= p10;
}
}
n >>= 1;
p10 *= p10;
}
if (!is_real(number))
{
set_errno(ERANGE);
}
errout:
if (endptr)
{
*endptr = p;
}
return number;
}
#endif /* CONFIG_HAVE_DOUBLE */