By using this site, you agree to our updated Privacy Policy and our Terms of Use. Manage your Cookies Settings.
440,496 Members | 1,517 Online
Bytes IT Community
+ Ask a Question
Need help? Post your question and get tips & solutions from a community of 440,496 IT Pros & Developers. It's quick & easy.

user defined function that converts string to float

P: n/a
hi,
I need user defined function that converts string to float in c.
since the library function atof and strtod occupies large space in
my processor memory I can't use it in my code.
regards,
Karthi

Jan 26 '06 #1
Share this Question
Share on Google+
6 Replies


P: n/a
karthi wrote:
hi,
I need user defined function that converts string to float in c.
since the library function atof and strtod occupies large space in
my processor memory I can't use it in my code.


Sounds a bit weird, linkers will normally strip out unused functions [from a
library] to create your executable. So, it *should* be that the size of the
executable will be optimal, i.e., if you don't link in either of the
functions you mention, but write your own - that's a similar size, you'll
not gain anything.

Also, if you can use sscanf this will do what you want ...

char s[] = "3.14157";

float f;

sscanf(s, "%f", &f);


--
================================================== =============
In an attempt to reduce 'unwanted noise' on the 'signal' ...

Disclaimer:

Any comment/code I contribute might =NOT= be 100% portable, nor
semantically correct [read - 'not 100% pedantically correct'].
I don't care too much about that though, and I reckon it's the
same with most 'visitors' here. However, rest assured that any
'essential' (?) corrections WILL almost certainly appear v.soon
[read - 'to add noise as they see fit, *a pedant* will be along
shortly'].

WARNINGS: Always read the label. No beside-the-point minutiae
filter supplied. Keep away from children. Do not ignite.
================================================== =============
Jan 26 '06 #2

P: n/a
On 26 Jan 2006 01:06:35 -0800, in comp.lang.c , "karthi"
<ke******@gmail.com> wrote:
hi,
I need user defined function that converts string to float in c.
since the library function atof and strtod occupies large space in
my processor memory I can't use it in my code.


Anything you write in C is likely to be at least as large in memory,
you may need to use assembler.
I guess you could walk down the array of chars, converting each one to
an integer, then summing when you were done. Here's an implementation
which only works for whole numbers, I leave it as an exercise for the
reader to fix the bugs, implement decimal support etc.

#include <stdio.h>

int main ()
{
char* t="143";
char* s = t;
double d=0;
while (*s)
{
d = d*10;
d += *s-'0';
s++;
}
printf ("%s = %f", t, d);
}
Mark McIntyre
--
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----
Jan 26 '06 #3

P: n/a
karthi wrote:
hi,
I need user defined function that converts string to float in c.
since the library function atof and strtod occupies large space in
my processor memory I can't use it in my code.


It is likely that strtod() is implemented with pretty
good efficiency, and unlikely that you will be able to
re-implement all its features in significantly less memory.

However, you may be able to write a smaller function
if you are willing to give up some features of strtod().
For example, you may not care about locale sensitivity.
Perhaps you can accept sloppy rounding, especially with
very small or very large values. You may choose to convert
"42" but not "4.2e1" and "4200e-3". And so on -- if you
can live with less functionality, you may be able to use
less memory.

So: What are you willing to do without?

--
Eric Sosman
es*****@acm-dot-org.invalid
Jan 27 '06 #4

P: n/a
use sprintf see prinf format info

Jan 28 '06 #5

P: n/a
joev wrote:
use sprintf see prinf format info


Now this is the least sensible post that I've seen in a while!
What are you talking about, in which language, to whom???

See this advice, and do follow the link!

"If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell.org/google/>

Cheers

Vladimir

Jan 29 '06 #6

P: n/a

karthi wrote:
hi,
I need user defined function that converts string to float in c.
since the library function atof and strtod occupies large space in
my processor memory I can't use it in my code.
regards,
Karthi


The following is a quick hack:

/* strtold.c - code for the atof, strtod, strtof, and strtold functions

AUTHOR: Gregory Pietsch

DESCRIPTION:

The strtod, strtof, and strtold functions convert the initial
portion of the
string pointed to by nptr to double, float, and long double
representations,
respectively. First, they decompose the input string into three
parts: an
initial, possibly empty, sequence of white-space characters (as
specified by
the isspace function), a subject sequence resembling a
floating-point
constant or representing infinity or NaN, and a final sequence of
one or
more unrecognized characters, including the terminating null
character of
the input string. Then, they attempt to convert the subject string
to a
floating-point number, and return the result.

The expected form of the subject sequence is an optional plus or
minus sign,
then one of the following:

- a nonempty sequence of decimal digits optionally containing a
decimal-
point character, then an optional exponent part as defined in
6.4.4.2;

- a 0x or 0X, then a nonempty sequence of hexadecimal digits
optionally
containing a decimal-point character, then an optional binary
exponent
part as defined in 6.4.4.2;

- one of INF or INFINITY, ignoring case

- one of NAN or NAN(n-char-sequence_opt), ignoring case in the NAN
part,
where:

n-char-sequence:
digit
nondigit
n-char-sequence digit
n-char-sequence non-digit

The subject sequence is defined as the longest initial subsequence
of the
input string, starting with the first non-white-space character,
that is of
the expected form. The subject sequence contains no characters if
the input
string is not of the expected form.

If the subject sequence has the expected form for a floating-point
number,
the sequence of characters starting with the first digit or the
decimal-
point character (whichever comes first) is interpreted as a floating

constant according to the rules of 6.4.4.2, except that the
decimal-point
character is used in place of a period, and that if neither an
exponent part
nor a decimal-point character appears in a decimal floating-point
number,
or if a binary exponent part does not appear in a hexadecimal
floating-point
number, an exponent part of the appropriate type with value zero is
assumed
to follow the last digit in the string. If the subject sequence
begins with
a minus sign, the sequence is interpreted as negated. (It is
unspecified
whether a minus-signed sequence is converted to a negative number
directly
or by negating the value resulting from converting the corresponding
unsigned sequence [see F.5]; the two methods may yield different
results if
rounding is toward positive or negative infinity. In either case,
the
functions honor the sign of zero if floating-point arithmetic
supports
signed zeros.) A character sequence INF or INFINITY is interpreted
as an
infinity, if representable in the return type, else like a floating
constant
that is too large for the range of the return type. A character
sequence
NAN or NAN(n-char-sequence_opt), is interpreted as a quiet NaN, if
supported
in the return type, else like a subject sequence part that does not
have the
expected form; the meaning of the n-char-sequences is
implementation-defined
(an implementation may use the n-char-sequence to determine extra
information to be represented in the NaN's significand). A pointer
to the
final string is stored in the object pointed to by endptr, provided
that
endptr is not a null pointer.

If the subject string has the hexadecimal form and FLT_RADIX is a
power of
2, the value resulting from the conversion is correctly rounded.

In other than the "C" locale, additional locale-specific subject
sequences
may be accepted.

If the subject sequence is empty or does not have the expected form,
no
conversion is performed; the value of nptr is stored in the object
pointed
to by endptr, provided that endptr is not a null pointer.

RECOMMENDED PRACTICE:

If the subject sequence has the hexadecimal form, FLT_RADIX is not a
power
of 2, and the result is not exactly representable, the result should
be one
of the two numbers in the appropriate internal format that are
adjacent to
the hexadecimal floating source value, with the stipulation that the
error
should have the correct sign for the current rounding direction.

If the subject sequence has the decimal form and at most DECIMAL_DIG
(defined in <float.h>) significant digits, the result should be
correctly
rounded. If the subject sequence D has the decimal form and more
than
DECIMAL_DIG significant digits, consider the two bounding, adjacent
decimal strings L and U, both having DECIMAL_DIG significant digits,
such
that the values of L, D, and U satisfy L <= D <= U. The result
should be
one of the (equal or adjacent) values that would be obtained by
correctly
rounding L and U according to the current rounding direction, with
the extra
stipulation that the error with respect to D should have a correct
sign for
the current rounding direction. (DECIMAL_DIG, defined in <float.h>,
should
be significantly large that L and U will usually round to the same
internal
floating value, but if not will round to adjacent values.)

RETURNS:

The functions return the converted value, if any. If no conversion
could be
performed, zero is returned. If the correct value is outside the
range of
representable values, plus or minus HUGE_VAL, HUGE_VALF, or
HUGE_VALL is
returned (according to the return type and sign of the value), and
the value
of the macro ERANGE is stored in errno. If the result underflows
(7.12.1),
the functions return a value whose magnitude is no greater than the
smallest
normalized positive number in the return type; whether errno
acquires the
value ERANGE is implementation-defined.

COPYRIGHT NOTICE:

This file is placed into the public domain by the author, Gregory
Pietsch.
Do with it what you wish; just don't pretend that you wrote it.
*/

/* includes needed by this file */
#include <ctype.h>
#include <errno.h>
#include <float.h>
#include <limits.h>
#include <locale.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>

/* defines */

/* SIG_MAX: the maximum number of significant digits we have. The
maximum
number of significant digits in a long double must be at least 35,
which is the number of significant digits in an IEEE quad precision
floating-point number (113 * log10(2.0), rounded up). */
#define SIG_MAX 40

/* _Memcasecmp: return a case-insensitive comparison of two areas of
memory. */
static int
_Memcasecmp (const void *s1, const void *s2, size_t n)
{
const unsigned char *su1, *su2;

for (su1 = s1, su2 = s2; 0 < n; ++su1, ++su2, --n)
{
if (toupper (*su1) != toupper (*su2))
return (*su1 < *su2 ? -1 : +1);
}
return 0;
}

/* _Ldmul: multiply y by *px with checking */
static int
_Ldmul(long double *px, long double y)
{
int lexp;
long double ld;

ld = frexpl(*px, &lexp) * y;
errno = 0;
*px = ldexpl(ld, lexp); /* ldexpl can overflow */
return errno != 0 ? -1 : 0;
}

/* _Ldtento: compute x * 10^n, paranoid style */
static long double
_Ldtento(long double x, int n)
{
long double factor, fac10;
int errx;
unsigned nu;

if (n == 0 || x == 0.0L)
return x;
factor = 1.0L;
if (n < 0)
{
/* scale down */
nu = -(unsigned)n;
for (fac10 = 10.0L; 0 < nu; nu >>= 1, fac10 *= fac10)
{
if (nu & 1)
factor *= fac10;
}
errx = _Ldmul(&x, 1.0L/factor);
}
else
{
/* scale up */
for (fac10 = 10.0L; 0 < n; n >>= 1, fac10 *= fac10)
{
if (n & 1)
factor *= fac10;
}
errx = _Ldmul(&x, factor);
}
if (0 < errx)
errno = ERANGE;
return x;
}

/* _Stold: return the classification of the floating-point number
(FP_ZERO
if there's no number; if there's a zero, return FP_NORMAL).
The pld parameter is a possibly-returned long double;
the pnan parameter is the n-char-sequence returned if we're
returning FP_NAN. */
static int
_Stold (const char *s, char **endptr, long double *pld, char **pnan)
{
static const char hexits[] = {
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c',
'd', 'e',
'f'
};
const char point = localeconv ()->decimal_point[0];
const char *sc;
char buf[SIG_MAX];
char sign;
long double x, fac, facpow;
int ndigit, nsig, nzero, olead, opoint, base;
size_t m;
char *p;
const char *pc;
int n;
unsigned long lo[SIG_MAX / 8 + 1], *pl;
short sexp;
long lexp;
const char *scsav, esign;

/* Get past the spaces. */
for (sc = s; isspace (*sc); ++sc)
;
/* Get past the initial sign. */
sign = (*sc == '-' || *sc == '+') ? *sc++ : '+';
/* Do we have INFINITY or INF? */
if (_Memcasecmp (*sc, "INFINITY", m = 8) == 0
|| _Memcasecmp (*sc, "INF", m = 3) == 0)
{
if (endptr)
*endptr = sc + m;
*pld = (sign == '-') ? -1.0L : +1.0L;
return FP_INFINITE;
}
/* Do we have NAN or NAN(nan-char-sequence_opt)? */
if (_Memcasecmp (*sc, "NAN(", m = 4) == 0
|| _Memcasecmp (*sc, "NAN", m = 3) == 0)
{
sc += m;
if (m == 4)
{
/* pick off the optional n-char-sequence */
p = strchr (sc, ')');
if (p == 0)
sc--; /* pretend the '(' doesn't belong */
else if (p == sc)
{
/* no n-char-sequence */
*pnan = 0;
sc++;
}
else
{
/* This could be a little more meticulous... */
*pnan = malloc ((p - sc) + 1);
if (*pnan == 0)
sc--; /* out of memory */
else
{
memcpy (*pnan, sc, (p - sc) - 1);
(*pnan)[p - sc] = '\0';
}
}
}
else
*nan = 0;
if (endptr)
*endptr = sc;
*pld = (sign == '-') ? -1.0L : +1.0L;
return FP_NAN;
}
/* Do we have a hexadecimal floating-point constant? */
if (_Memcasecmp (*sc, "0X", 2) == 0)
{
sc += 2;
base = 16;
}
else
base = 10;
/* get the digits/hexits before the exponent */
for (ndigit = nsig = nzero = 0, olead = opoint = -1;; ++sc)
{
if (*sc == point)
{
/* found a decimal point */
if (0 <= opoint)
break; /* already seen point */
else
opoint = ndigit;
}
else if (*sc == '0')
{
/* saw a zero */
++nzero;
++ndigit;
}
else if ((base == 16 && !isxdigit (*sc))
|| (base == 10 && !isdigit (*sc)))
break;
else
{
/* found a nonzero digit */
if (olead < 0)
olead = nzero;
else
{
/* deliver zeros */
for (; 0 < nzero && nsig < SIG_MAX; --nzero)
buf[nsig++] = 0;
}
++ndigit;
if (nsig < SIG_MAX)
{
/* deliver digit */
if (base == 10)
buf[nsig++] = *sc - '0';
else
{
p = strchr (hexits, tolower (*sc));
buf[nsig++] = p - hexits;
}
}
}
}
if (ndigit == 0)
{
/* no digits? return not-a-long double */
if (endptr)
*endptr = (char *) s;
return FP_ZERO;
}
/* skip trailing digits */
for (; 0 < nsig && buf[nsig - 1] == 0; --nsig)
;
/* compute significand */
*pc = buf;
pl = lo + (nsig >> 3);
for (*pl = 0, n = nsig; 0 < n; --n)
{
if ((n & 7) == 0)
*--pl = *pc++;
else
*pl = *pl * base + *pc++;
}
fac = facpow = (base == 10) ? 1e8L : +4294967296.0L;
for (x = (long double) *lo, n = 0; ++n <= (nsig >> 3);)
{
if (lo[n] != 0UL)
x += fac * lo[n];
fac *= facpow;
}
/* fold in any explicit exponent */
lexp = 0;
if ((base == 10 && (*sc == 'e' || *sc == 'E'))
|| (base == 16 && (*sc == 'p' || *sc == 'P')))
{
*scsav = sc;
esign = *++sc == '+' || *sc == '-' ? *sc++ : '+';
if (!isdigit (*sc))
*sc = *scsav; /* ill-formed exponent */
else
{
/* exponent looks valid */
for (; isdigit (*sc); ++sc)
if (lexp < 10000)
lexp = lexp * 10 + (*sc - '0');
/* else overflow */
if (esign == '-')
lexp = -lexp;
}
}
if (endptr)
*endptr = (char *) sc;
if (opoint < 0)
lexp += ndigit - nsig;
else
lexp += opoint - olead - nsig;
sexp =
(lexp <
SHRT_MIN) ? SHRT_MIN : ((lexp < SHRT_MAX) ? (short) lexp :
SHRT_MAX);
if (base == 10)
*pld = _Ldtento (x, sexp);
else
*pld = ldexpl (x, (int) (sexp) << 2);
if (sign == '-')
*pld = -*pld;
return FP_NORMAL;
}

/* exported functions */

/* atof */
double (atof) (const char *nptr)
{
return strtod (nptr, 0);
}

/* strtod */
double (strtod) (const char *restrict nptr, char **restrict endptr)
{
long double ld;
char *nan_arg = 0;
double d;

switch (_Stold (nptr, endptr, &ld, &nan_arg))
{
case FP_NORMAL:
default:
if ((ld < 0.0L ? -ld : ld) > DBL_MAX)
{
errno = ERANGE;
return (ld < 0.0L) ? -HUGE_VAL : HUGE_VAL;
}
else
return (double) ld;
case FP_ZERO:
return 0.0;
case FP_NAN:
d = copysign (nan (nan_arg), (double) ld);
if (nan_arg != 0)
free (nan_arg);
return d;
case FP_INFINITE:
return ld < 0.0L ? -HUGE_VAL : HUGE_VAL;
}
}

/* strtof */
float (strtof) (const char *restrict nptr, char **restrict endptr)
{
long double ld;
char *nan_arg = 0;
float f;

switch (_Stold (nptr, endptr, &ld, &nan_arg))
{
case FP_NORMAL:
default:
if ((ld < 0.0L ? -ld : ld) > FLT_MAX)
{
errno = ERANGE;
return (ld < 0.0L) ? -HUGE_VALF : HUGE_VALF;
}
else
return (float) ld;
case FP_ZERO:
return 0.0F;
case FP_NAN:
f = copysignf (nanf (nan_arg), (float) ld);
if (nan_arg != 0)
free (nan_arg);
return f;
case FP_INFINITE:
return ld < 0.0L ? -HUGE_VALF : HUGE_VALF;
}
}

/* strtold */
long double (strtold) (const char *restrict nptr, char **restrict
endptr)
{
long double ld;
char *nan_arg = 0;

switch (_Stold (nptr, endptr, &ld, &nan_arg))
{
case FP_NORMAL:
default:
return ld;
case FP_ZERO:
return 0.0;
case FP_NAN:
ld = copysignl (nanl (nan_arg), ld);
if (nan_arg != 0)
free (nan_arg);
return ld;
case FP_INFINITE:
return ld < 0.0L ? -HUGE_VALL : HUGE_VALL;
}
}

/* END OF FILE */

Gregory Pietsch

Feb 2 '06 #7

This discussion thread is closed

Replies have been disabled for this discussion.