round result of floating point calcualtion

Yes it is an integer value which I try to compute. The problem when I divide the values is the following.
The value 2.147483648E16 is fix but the second value is variable from 70700000, 70700001, 70700002 .....124999999, 125000000. When I pre-divide this value then the value 124999999 looks like this 124. Then my problem is much bigger because many results are the same.

Jan

Yes it is an integer value which I try to compute. The problem when I divide the values is the following.
The value 2.147483648E16 is fix but the second value is variable from 70700000, 70700001, 70700002 .....124999999, 125000000. When I pre-divide this value then the value 124999999 looks like this 124. Then my problem is much bigger because many results are the same.

Jan

The following URL

http://docs.sun.com/source/806-3568/ncg_goldberg.html

links to an article titled, "What Every Computer Scientist Should Know About Floating-Point Arithmetic."

This article addresses most of the floating-point questions posed on this forum.

Jon

That looks like you actually need arbitrary precision arithmetics A rough outline: recall how you learned to do multiplication and division on multi-digit numbers in elementary school. Apply same principles to very large numbers, using bytes or ints instead of decimal digits.

Let's say we use unsigned 16-bit ints for "digits". That makes your dividend a 4-digit number, and all your divisors 2-digit numbers.

So you would divide pairwise, compute remainders and accumulate results.

There are multiple precision arithmetics packages out there that help with this --- I'm not aware of any working on 8051s though.

You will find a set of 64-bit functions using only 32-bit variables here:

ftp.embedded.com/.../crenshaw98.txt

I have solved the problem.
Here is the solution which I use. I hope I will get no problem with the timing.

unsigned long test_value;
unsigned int result;
unsigned long test_freq;


         dds_word.long_dds = 0;
         test_value = 0x04C4B400;
         for (i=0; i<7; i++)
            {
            result = test_value / test_freq;
            test_value = test_value - (result * test_freq);
            test_value = test_value << 4;
            dds_word.long_dds += result;
            dds_word.long_dds = dds_word.long_dds << 4;
            }
         result = test_value / test_freq;
         dds_word.long_dds += result;