Re: Reg: gcc option for printing large number (large double)
On Mon, Sep 09, 2013 at 10:11:21AM +0530, Balamurugan wrote:
I have an issue in printing a large number in a c program. Please
find below the code snippet :
#include math.h
int main()
{
double temp = 0.0;
temp = pow(2, 2000);
printf(The value of temp is %lf\n, temp);
return 0;
}
I compiled and ran as below:
[balamurugan@balamurugan C_Programs]$ gcc test.c -o test
[balamurugan@balamurugan C_Programs]$ ./test
The value of temp is _inf_
But for the same expression, I am able to get the value from python,
[balamurugan@balamurugan C_Programs]$ python
Python 2.6.6 (r266:84292, Feb 22 2013, 00:00:18)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-3)] on linux2
Type help, copyright, credits or license for more information.
pow(2,2000)
11481306952742545242328332011776819840223177020886952004776427368257662613923703138566594863165062699184459646389874627734471189608630553314259313561666531853912998914531228688779148240044871428926990063486244781615463646388363947317026040466353970904996558162398808944629605623311649536164221970332681344168908984458505602379484807914058900934776500429002716706625830522008132236281291761267883317206598995396418127021779858404042159853183251540889433902091920554957783589672039160081957216630582755380425583726015528348786419432054508915275783882625175435528800822842770817965453762184851149029376L
I know that in gcc, there is an option for getting this done. Can
any body help with that option?
This is outside the precision of double-precision floating point. Have
a look into multi-precision arithmetic libraries such as libgmp
(libgmp-dev). Or if you also do C++, see Boost.Multiprecision, which
wraps the GMP types nicely so you can use them as regular primitives.
Regards,
Roger
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Re: Reg: gcc option for printing large number (large double)
On Mon, Sep 9, 2013 at 2:40 PM, Joel Rees joel.r...@gmail.com wrote:
On Mon, Sep 9, 2013 at 1:41 PM, Balamurugan emailstorb...@gmail.com wrote:
Hi,
I have an issue in printing a large number in a c program. Please find below
the code snippet :
#include math.h
int main()
{
double temp = 0.0;
temp is a double. In your ordinary environment, doubles are stored in
64 bits. But that's 64 bits total, and you have to have some room for
the exponent. In some environments, you have 128 bits for doubles, but
that's not the usual case.
Checking the foat.h header should give you some idea how large a
number you can store in a double. Except I don't see any sign of
float.h in /usr/include. Hmm.
Checking my copy of the old C89 standard, doubles are only guaranteed
to have more than 10 digits accuracy with a maximum storeable value of
at least 10 to the 37th power.
You can check these with a short C program. See below.
temp = pow(2, 2000);
2 to the 2000 power is, at any rate, at least 2000 bits long. That's
way more than 128 bits even.
Counting the digits of output from Python, that's way more than 37
decimal digits.
printf(The value of temp is %lf\n, temp);
return 0;
}
Here's the program:
-
#include stdio.h
#include stdlib.h
#include float.h
#include math.h
int main( int argc, char * argv[] )
{
double temp;
long double ltemp;
printf( max double digits: %d, double exponent %d\n, DBL_DIG,
DBL_MAX_10_EXP );
printf( max double value: %Lf\n, (long double) DBL_MAX );
ltemp = pow( 2, 2000 );
temp = pow( 2, 2000 );
printf( 2^2000 as double: %f\n, temp );
printf( 2^2000 as long double: %Lf\n, ltemp );
return EXIT_SUCCESS;
}
-
Not sure why neither man -k nor whereis can find float.h, but it compiles okay.
Here's the output on my machine (Intel AMD64 running 64 bit today):
-
jwr@fun:~/work/mathgames$ cc -o float_h -Wall float_h.c
jwr@fun:~/work/mathgames$ ./float_h
max double digits: 15, double exponent 308
max double value:
179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368.00
2^2000 as double: inf
2^2000 as long double: inf
-
I compiled and ran as below:
[balamurugan@balamurugan C_Programs]$ gcc test.c -o test
[balamurugan@balamurugan C_Programs]$ ./test
The value of temp is inf
inf, borrowed to invoke the idea of infinity, indicates that the
number is too large to store.
But for the same expression, I am able to get the value from python,
[balamurugan@balamurugan C_Programs]$ python
Python 2.6.6 (r266:84292, Feb 22 2013, 00:00:18)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-3)] on linux2
Type help, copyright, credits or license for more information.
pow(2,2000)
11481306952742545242328332011776819840223177020886952004776427368257662613923703138566594863165062699184459646389874627734471189608630553314259313561666531853912998914531228688779148240044871428926990063486244781615463646388363947317026040466353970904996558162398808944629605623311649536164221970332681344168908984458505602379484807914058900934776500429002716706625830522008132236281291761267883317206598995396418127021779858404042159853183251540889433902091920554957783589672039160081957216630582755380425583726015528348786419432054508915275783882625175435528800822842770817965453762184851149029376L
As you can see there are just a few too many digits in 2^2000.
Python has unlimited precision math (as do ruby and bc, among others).
Some architectures will provide more bits for long double in C, and
maybe even some for double. But those are the exception.
I know that in gcc, there is an option for getting this done. Can any body
help with that option?
Not so much an option as a library, that is not part of the standard.
Several libraries, in fact. I don't remember their names right
off-hand, don't seem to have them loaded in my system, either. Looking
up BigInt led me to them in the past.
Thanks and Regards,
Balamurugan R
There is a C newsgroup that would likely be more helpful.
comp.lang.c is the newsgroup.
Searching google on c big float pulled up this page in stackoverflow:
http://stackoverflow.com/questions/6145329/c-efficient-big-floats
and reminded me of one of the libraries I've seen, gmp. There is a
link into wikipedia with more information and other libraries.
Unlimited precision is not as straightforward as one would like.
HTH
--
Joel Rees
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Re: Reg: gcc option for printing large number (large double)
On 09/09/13 07:21, Joel Rees wrote: snip code and stuff Not sure why neither man -k nor whereis can find float.h, but it compiles okay. dom@oz:~$ locate float.h /usr/lib/gcc/i486-linux-gnu/4.6/include/float.h /usr/lib/gcc/i486-linux-gnu/4.7/include/float.h /usr/lib/pymodules/python2.6/numpy/core/include/numpy/halffloat.h /usr/lib/pymodules/python2.7/numpy/core/include/numpy/halffloat.h /usr/share/pyshared/numpy/core/include/numpy/halffloat.h whereis looks on the PATH for a command. float.h isn't a command. It does also look for manpages, but... It does have a manpage: http://manpages.debian.net/cgi-bin/man.cgi?query=float.h but perhaps you don't have it installed. I certainly don't. -- Dom -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/522d7707.7090...@rpdom.net
Re: Reg: gcc option for printing large number (large double)
On Mon, Sep 09, 2013 at 08:21:43AM +0100, Dom wrote: It does have a manpage: http://manpages.debian.net/cgi-bin/man.cgi?query=float.h root@tal:~# apt-cache show manpages-dev but perhaps you don't have it installed. I certainly don't. root@tal:~# apt-cache policy manpages-dev -- If you're not careful, the newspapers will have you hating the people who are being oppressed, and loving the people who are doing the oppressing. --- Malcolm X -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/20130909120058.GE25870@tal
Re: Reg: gcc option for printing large number (large double)
On 2013-09-09, Joel Rees joel.r...@gmail.com wrote: It does have a manpage: http://manpages.debian.net/cgi-bin/man.cgi?query=float.h It's funny, I was sure I had gotten that particular man page before. root@tal:~# apt-cache show manpages-dev You don't need to be root, by the way, to apt-cache your way around. Just a side note for anyone who might be reading the thread and thinking otherwise by example. -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/slrnl2s4l9.3op.cu...@einstein.electron.org
Re: Reg: gcc option for printing large number (large double)
On Mon, Sep 9, 2013 at 4:21 PM, Dom to...@rpdom.net wrote: On 09/09/13 07:21, Joel Rees wrote: snip code and stuff Not sure why neither man -k nor whereis can find float.h, but it compiles okay. dom@oz:~$ locate float.h /usr/lib/gcc/i486-linux-gnu/4.6/include/float.h /usr/lib/gcc/i486-linux-gnu/4.7/include/float.h /usr/lib/pymodules/python2.6/numpy/core/include/numpy/halffloat.h /usr/lib/pymodules/python2.7/numpy/core/include/numpy/halffloat.h /usr/share/pyshared/numpy/core/include/numpy/halffloat.h whereis looks on the PATH for a command. float.h isn't a command. It does also look for manpages, but... whereis picks up stuff in /usr/include and /usr/lib, as well. It does have a manpage: http://manpages.debian.net/cgi-bin/man.cgi?query=float.h but perhaps you don't have it installed. I certainly don't. -- Dom I actually do have manpages-dev installed, so I can get a man page on fgetc, but it still doesn't give me a man page for stuff in float.h. It's two am here. I'm going to bed. -- Joel Rees -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/CAAr43iNwX-z8=4g+dp-jxyo+ngfftmithsmnmjyfmfmsrma...@mail.gmail.com
Re: Reg: gcc option for printing large number (large double)
On Mon, Sep 9, 2013 at 9:00 PM, Chris Bannister cbannis...@slingshot.co.nz wrote: On Mon, Sep 09, 2013 at 08:21:43AM +0100, Dom wrote: It does have a manpage: http://manpages.debian.net/cgi-bin/man.cgi?query=float.h It's funny, I was sure I had gotten that particular man page before. root@tal:~# apt-cache show manpages-dev but perhaps you don't have it installed. I certainly don't. root@tal:~# apt-cache policy manpages-dev manpages-dev is loaded on my machine. But digging in, I see something about glibc-doc. Using synaptic because I'm lazy, I see that glibc-doc has been split, and glibc-doc-reference contains most of the documentation for glibc. Split because of license issues, it says. And glibc-doc is in the usual repository, but glibc-doc-reference is not. So I enable contrib and non-free because it's late and I don't care which one has glibc-doc-reference and now I can load glibc-doc-reference. But still no response when I do man float.h or man -k DBL_DIG or info DBL_DIG. man fgetc works. So does info fgetc My memory is that it worked with only manpages-dev installed. But even with glibc-doc-reference installed, nothing on the macros in limits.h or float.h. Or locale.h. But man HUGE_VAL brings up the man page for the constants in math.h. And I think it did with just manpages-dev. I wonder what gives here. -- If you're not careful, the newspapers will have you hating the people who are being oppressed, and loving the people who are doing the oppressing. --- Malcolm X -- Joel Rees -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/CAAr43iNbLjv0=7g3t6-JNK=4preqlqu4hq2h+atcfs4-3br...@mail.gmail.com
Re: Reg: gcc option for printing large number (large double)
DEC_EVAL_METHOD
Can't seem to turn this loose.
On Tue, Sep 10, 2013 at 1:51 AM, Joel Rees joel.r...@gmail.com wrote:
On Mon, Sep 9, 2013 at 4:21 PM, Dom to...@rpdom.net wrote:
On 09/09/13 07:21, Joel Rees wrote:
snip code and stuff
Not sure why neither man -k nor whereis can find float.h, but it compiles
okay.
dom@oz:~$ locate float.h
/usr/lib/gcc/i486-linux-gnu/4.6/include/float.h
/usr/lib/gcc/i486-linux-gnu/4.7/include/float.h
/usr/lib/pymodules/python2.6/numpy/core/include/numpy/halffloat.h
/usr/lib/pymodules/python2.7/numpy/core/include/numpy/halffloat.h
/usr/share/pyshared/numpy/core/include/numpy/halffloat.h
whereis looks on the PATH for a command. float.h isn't a command. It does
also look for manpages, but...
whereis picks up stuff in /usr/include and /usr/lib, as well.
It does have a manpage:
http://manpages.debian.net/cgi-bin/man.cgi?query=float.h
but perhaps you don't have it installed. I certainly don't.
--
Dom
I actually do have manpages-dev installed, so I can get a man page on
fgetc, but it still doesn't give me a man page for stuff in float.h.
Now that I see that man works for the functions and macros and not for
the header name (But why wouldn't man-k pick that up?), I do a man
pow and notice there is a powl() function that looks like it might
work but maybe doesn't:
---
#include stdio.h
#include stdlib.h
#include float.h
#include math.h
int main( int argc, char * argv[] )
{
double temp;
long double ltemp;
printf( max double digits: %d, double exponent %d\n, DBL_DIG,
DBL_MAX_10_EXP );
printf( max double value: %Lf\n, (long double) DBL_MAX );
temp = pow( 2, 2000 );
ltemp = powl( 2, 2000 );
printf( 2^2000 as double: %f\n, temp );
printf( 2^2000 as long double: %Lf\n, ltemp );
ltemp = ltemp + 1.0;
printf( 2^2000 + 1 as long double: %Lf\n, ltemp );
return EXIT_SUCCESS;
}
---
which prints out the value of 2^2000 okay, but fails to increment it.
Which makes sense, since we have no reason to believe long double ever
gets 2000 bits of significance, but powers of two should be accurately
stored up to the limit of the exponent.
Thus the need for GMP or MPFR or similar libraries. (Or you can just
do it in python. ;)
http://en.wikipedia.org/wiki/GNU_Multi-Precision_Library
and
http://en.wikipedia.org/wiki/MPFR
I note:
cat /usr/lib/gcc/x86_64-linux-gnu/4.7/include/float.h
a constant, DEC_EVAL_METHOD,
#undef DEC_EVAL_METHOD
#define DEC_EVAL_METHOD2
might force all operations and constants to the range and precision
of the _Decimal128 type, which might be of interest for compiling
environments which do not make long doubles longer than doubles -- a
kind of last chance on those systems. Unless he only needs the
constant, and doesn't need precision/accuracy, the OP is going to want
GMP or MPFR or the like, if python can't do his job.
Since I seem to be convincing myself against my better judgment that I
have time, and since I've always wanted to play with the
multiprecision stuff, I'm going to install libgmp-dev and read the
website
http://gmplib.org/
and risk stealing the OP's opportunity for learning.
-
#include stdio.h
#include stdlib.h
#include float.h
#include math.h
#include gmp.h /* NOT a standard header! */
int main( int argc, char * argv[] )
{
double temp;
long double ltemp;
mpz_t z_result; /* Doing it with arbitrary precision integers. */
mpf_t f_result; /* Doing it with arbitrary precision floats. */
mpf_t f_2; /* Don't seem to have mpf_ui_pow_ui(). */
printf( max double digits: %d, double exponent %d\n, DBL_DIG,
DBL_MAX_10_EXP );
printf( max double value: %Lf\n, (long double) DBL_MAX );
temp = pow( 2, 2000 );
ltemp = powl( 2, 2000 );
printf( 2^2000 as double: %f\n, temp );
printf( 2^2000 as long double: %Lf\n, ltemp );
ltemp = ltemp + 1.0;
printf( 2^2000 + 1 as long double: %Lf\n, ltemp );
mpz_init( z_result );
mpz_ui_pow_ui( z_result, 2, 2000 );
gmp_printf( \n integer 2^2000 is \n%Zd\n, z_result );
mpz_add_ui( z_result, z_result, 1 );
gmp_printf( \n integer 2^2000 + 1 is \n%Zd\n, z_result );
mpz_clear( z_result );
mpf_init2( f_result, 2500 ); /* A bit of extra room in the precision. */
mpf_init_set_ui( f_2, 2 );
mpf_pow_ui( f_result, f_2, 2000 );
gmp_printf( \n float 2^2000 is \n%Ff\n, f_result );
mpf_add_ui( f_result, f_result, 1 );
gmp_printf( \n float 2^2000 + 1 is \n%Ff\n, f_result );
mpf_clear( f_result );
return EXIT_SUCCESS;
}
-
Save it as float_h.c and compile it with
cc -o float_h -lgmp -Wall float_h.c
run it with
./float_h
--
Joel Rees
Look around, the leaves are green,
The grass is high, it's the springtime of my life!
Yeah! FUN!
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Reg: gcc option for printing large number (large double)
Hi,
I have an issue in printing a large number in a c program. Please find
below the code snippet :
#include math.h
int main()
{
double temp = 0.0;
temp = pow(2, 2000);
printf(The value of temp is %lf\n, temp);
return 0;
}
I compiled and ran as below:
[balamurugan@balamurugan C_Programs]$ gcc test.c -o test
[balamurugan@balamurugan C_Programs]$ ./test
The value of temp is _inf_
But for the same expression, I am able to get the value from python,
[balamurugan@balamurugan C_Programs]$ python
Python 2.6.6 (r266:84292, Feb 22 2013, 00:00:18)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-3)] on linux2
Type help, copyright, credits or license for more information.
pow(2,2000)
11481306952742545242328332011776819840223177020886952004776427368257662613923703138566594863165062699184459646389874627734471189608630553314259313561666531853912998914531228688779148240044871428926990063486244781615463646388363947317026040466353970904996558162398808944629605623311649536164221970332681344168908984458505602379484807914058900934776500429002716706625830522008132236281291761267883317206598995396418127021779858404042159853183251540889433902091920554957783589672039160081957216630582755380425583726015528348786419432054508915275783882625175435528800822842770817965453762184851149029376L
I know that in gcc, there is an option for getting this done. Can any
body help with that option?
Thanks and Regards,
Balamurugan R
Re: Reg: gcc option for printing large number (large double)
On Mon, Sep 9, 2013 at 1:41 PM, Balamurugan emailstorb...@gmail.com wrote:
Hi,
I have an issue in printing a large number in a c program. Please find below
the code snippet :
#include math.h
int main()
{
double temp = 0.0;
temp is a double. In your ordinary environment, doubles are stored in
64 bits. But that's 64 bits total, and you have to have some room for
the exponent. In some environments, you have 128 bits for doubles, but
that's not the usual case.
Checking the foat.h header should give you some idea how large a
number you can store in a double. Except I don't see any sign of
float.h in /usr/include. Hmm.
Checking my copy of the old C89 standard, doubles are only guaranteed
to have more than 10 digits accuracy with a maximum storeable value of
at least 10 to the 37th power.
temp = pow(2, 2000);
2 to the 2000 power is, at any rate, at least 2000 bits long. That's
way more than 128 bits even.
Counting the digits of output from Python, that's way more than 37
decimal digits.
printf(The value of temp is %lf\n, temp);
return 0;
}
I compiled and ran as below:
[balamurugan@balamurugan C_Programs]$ gcc test.c -o test
[balamurugan@balamurugan C_Programs]$ ./test
The value of temp is inf
inf, borrowed to invoke the idea of infinity, indicates that the
number is too large to store.
But for the same expression, I am able to get the value from python,
[balamurugan@balamurugan C_Programs]$ python
Python 2.6.6 (r266:84292, Feb 22 2013, 00:00:18)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-3)] on linux2
Type help, copyright, credits or license for more information.
pow(2,2000)
11481306952742545242328332011776819840223177020886952004776427368257662613923703138566594863165062699184459646389874627734471189608630553314259313561666531853912998914531228688779148240044871428926990063486244781615463646388363947317026040466353970904996558162398808944629605623311649536164221970332681344168908984458505602379484807914058900934776500429002716706625830522008132236281291761267883317206598995396418127021779858404042159853183251540889433902091920554957783589672039160081957216630582755380425583726015528348786419432054508915275783882625175435528800822842770817965453762184851149029376L
I know that in gcc, there is an option for getting this done. Can any body
help with that option?
Not so much an option as a library, that is not part of the standard.
Several libraries, in fact. I don't remember their names right
off-hand, don't seem to have them loaded in my system, either. Looking
up BigInt led me to them in the past.
Thanks and Regards,
Balamurugan R
There is a C newsgroup that would likely be more helpful.
--
Joel Rees
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