Post Reply 
Improve precision of float numbers
04-13-2019, 02:03 PM
Post: #7
RE: Improve precision of float numbers
(04-11-2019 10:10 AM)deetee Wrote:  Hi all!

I like to build small RPN calculators (ScArY, SCOTT, ARC) with AVR microcontrollers (which are easy to program).

Unfortunately these microcontrollers support float numbers with 4 byte single precision (due IEEE-754) only. That means they support a precision of 6 to 7 decimal digits.

Now I would like to improve this precision to at least 9 decimal digits. The only idea I have is to define a new number format (struct) to separate mantissa and exponent:

struct real {
  long m;
  int8_t e;

But now I have to "reinvent" every mathematical operation like adding two numbers (the following code works, but is far from beeing efficient):

void realadd(real * res, real a, real b) {
  if (a.e >= b.e) {
    b.m /= _pow10(a.e-b.e);
    res->m = a.m + b.m;
    res->e = a.e;
  else {
    a.m /= _pow10(b.e-a.e);
    res->m = a.m + b.m;
    res->e = b.e;

Looking forward to transzendent functions or complex numbers I feel overstrained.

Do you have any other idea how to raise the precision with less effort?

Thanks for any idea.

What I did was to to use uint64_t (which gcc does support) and map it to a new float-64 type.
(see post:
Find all posts by this user
Quote this message in a reply
Post Reply 

Messages In This Thread
RE: Improve precision of float numbers - agarza - 04-13-2019 02:03 PM

User(s) browsing this thread: 1 Guest(s)