472,145 Members | 1,389 Online
Bytes | Software Development & Data Engineering Community
Post +

Home Posts Topics Members FAQ

Join Bytes to post your question to a community of 472,145 software developers and data experts.

storing a long in a float with same precision on Solaris 64bit OS

On Solaris 64-bit:

sizeof(long) = 8
sizeof(double) = 8 !!!

So i figure i can't store a long with the same precision in a double.
But, when i create a long and assign its largest value to it, then
assign this to a double, then subtract the double from the long, I get
0.

I see from the include files the exponent is 11 bits. So the Mantissa
must be 53 (or less) bits. So how can the double store my long to the
same precision??

I've posted the code and output below.

Any help appreciated.

Nishant

------------------------------
#include <stdlib.h>
#include <iostream.h>
#include <stdio.h>

int main()
{
cout << sizeof(long) << endl;
cout << sizeof(double) << endl;
cout << sizeof(float) << endl;

long l = 0x7FFFFFFFFFFFFFFF;
//long l = 9223372036854775807LL;
cout << "l = " << l << endl;

// want to confirm l is indeed the largest long
long nl = l + 1;
cout << "nl = " << nl << endl;

double d = l;
cout << "d = " << d << endl;

double r = d / l;
cout << "r = " << r << endl;

double rr = l - d;
cout << "rr = " << rr << endl;

}

--------
output:

8
8
4
l = 9223372036854775807
nl = -9223372036854775808
d = 9.22337e+18
r = 1
rr = 0

-------------------
Nov 13 '05 #1
1 2605
Nishant Deshpande wrote:

On Solaris 64-bit:

sizeof(long) = 8
sizeof(double) = 8 !!!

So i figure i can't store a long with the same precision in a double.


You can store SOME longs in a double without loss os precision,
but definitely not all longs.

In a double, I believe that 13 bits are used for the exponent and
one for the sign. These take away from the mantissa, so the largest
64 bit long that can be represented as a double is 51 bits long
or

-(2^51) to (2^51) - 1

If you look at this a little more closely, it is actually less
than 1 in 2^13 of all valif 64 bit longs.

Erik
--
+-----------------------------------------------------------+
Erik de Castro Lopo no****@mega-nerd.com (Yes it's valid)
+-----------------------------------------------------------+
"The Internet interprets censorship as damage, and routes around it."
-- John Gilmore
Nov 13 '05 #2

This discussion thread is closed

Replies have been disabled for this discussion.

Similar topics

1 post views Thread by dan | last post: by
4 posts views Thread by Michael Mair | last post: by
15 posts views Thread by michael.mcgarry | last post: by
6 posts views Thread by James Thurley | last post: by
17 posts views Thread by kiplring | last post: by
10 posts views Thread by Bryan Parkoff | last post: by
67 posts views Thread by lcw1964 | last post: by
reply views Thread by leo001 | last post: by

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.