Help wanted

If you're using an 8-bit microprocessor, simply translate doing long division by hand into steps of subtract, store if positive/jump if negative, shift and bring in new bits. If you can't do long division by hand, you're hosed.

Thanks John, but in "C" language....??

If you use a C compiler, it probably knows how to do math with long values...

No dear Uwe, the 8bit PIC or AVR don't have 16bit math library....

What about "long long"? Depends on your compiler, but if it is available, it may be 64 bits wide.

If there is no suitable data type, then you need to handle the carry-out manually. Unfortunately C does not let you access a carry flag inside the CPU. So you got two choices: Make the most significant bit the carry-out and handle it manually or use inline assembly. Inline assembly is quite easy to handle for GCC.

But I think, we are very off-topic!

Ralf

Uwe,

I actually had a real problem finding something that would deal with 48 bit long words for integer division...and multiplication.

I like John's approach: write a program to do what you would do by hand (in whatever language you like).

I think for Ham radio, 2E48 is a bit overkill, unless you are doing coherent detection...

Aust> Roberto IZ5FCY wrote:

int can_solve_problem(usenet_poster *op) { if (op->can_do_long_division) { think(op); write(op, SOME_CODE); return 1; } else { hosed++; return 0; } }

Hi there

wrong! AVR GCC suports int (16bit) long, and long long.

Aurash

Roberto IZ5FCY wrote:

If your PIC doesn't have a math library that can handle the large numbers, do it with an array of 8-bit integers or chars. Loop through the 8-bit values the way you loop through the digits to do long division.

If your base frequency will never change, however, forget calculating

Thanks John..

--

Thanks Ralph!

I'm sorry, but before FPGA implementation... where I could find one large reunion of "great brain people" like this? :-)))

Bye..

Look for mailing lists. Look at the website of the compiler you use. If there is GCC available for your MCU, then its quite possible, that there is a mailing list - and a documentation and a FAQ...

Ralf

Use the shift and subtract method :

This method is suited for 16-bit but can be easily extended to your bit length.

Excelent point.

Why 48 bits? If you need to provide a 3Hz signal with 1ppm accuracy from a 100 MHz clock, that's roughly 35 bits. If the accuracy requirement is determined different from raw frequency, a limited number of bits could be used with a simple shift, much like a floating point value.

Thanks Austin but isn't an Ham project...in the Web we can find thousand projects/kits ready-to-use for Ham. Bye.

Roberto,

I build many ham kits for fun.

Good luck with your project!

Roberto IZ5FCY wrote: