Floating point - please enlighten me!

[mackrackit]

I have never used them, maybe they are OK.
http://www.awce.com/compare.htm

[Jerson]

Floating point is a limitation of the PBP compiler. Nothing to do with PICs in general. You can use a floating point library and get by, but the question is do you really really need it? Most times, you will be using compile time fractions which can be broken down into simple integer operations.

The most general work around is to find an equivalent fraction that can be represented in integer math. For example, if you need to do pi x d, you can do

(d * 22)/7 to get a value in integers
or
(d*220)/7 to get a value with 1 decimal place. Only now, you need to place the decimal point while displaying the value.

I use an utility called MISCEL from http://www.miscel.dk which allows you to compute integer equivalents of a fraction in various word sizes.

The liabilities of Floating Point
1 - Bulky code
2 - Very time intensive computing A single operation can take approx 2-300mS
3 - PBP does not support it

Of course, even the long support needs you to migrate your code to an 18F series

[mark30504]

Hello

Trying to use some floating point.

PIC16f886

I have tried it several ways by no real luck

I have an number that need to be mulitiplied by .2235 to get corrrect result

Result can be rounded back to integer

For example

number = 250 usually a varriable but have tried it this way for testing

I have tried

number * .2235 ( won't compile)

and

number * (1000/4474) Compiles but result is zero

Answer should be somewhere around 55.8

I am not sure if the math is not working or I can not just see the number

That is; once the number is computed it is sent out RS232, it would work best if it was a whole number between 0-255 at time of sending
in this case 56 would be great.

Not sure where the problem lies.

Should the math be working ?

Is so how do I round to a whole number ?

thanks

Mark

I have never used them, maybe they are OK.
http://www.awce.com/compare.htm

[pedja089]

Try to use DIV32.

Dummy VAR WORD
Number VAR BYTE
Result VAR BYTE
Dummy = Number * 1000
Result=DIV32 4474

[ronsimpson]

Not using a compiler, using a calculator.
Input=250 and you want about 1/4 of that.
250*.2235=55.875
With out using a decimal point!
250*223/1000=55.75 (I did not use 2235/10000)
If the input will fit into a byte and 223 fits into a byte. Then (byte * byte)=word and then word/1000=55.
If you need a input like 350 which is a word and/or you want to use 2235/10000 then you will need to do word*word and word**word to get two words or 32 bits. You might also look at word*/word to get 16 bits out of the middle of the 32 bits.

[mark30504]

Not using a compiler, using a calculator.
Input=250 and you want about 1/4 of that.
250*.2235=55.875
With out using a decimal point!

Yes, I always like the types of Stupid answer's one gets when asking a simple question.

Number is a variable and constantly changing.

As I said for example 250

This is just part of a longer calculation. If it was as simple as just putting a number I really wanted, I think I might of though of that....

I was just looking for the format to input numbers like .00044

thanks

Not using a compiler, using a calculator.
Input=250 and you want about 1/4 of that.
250*.2235=55.875
With out using a decimal point!
250*223/1000=55.75 (I did not use 2235/10000)
If the input will fit into a byte and 223 fits into a byte. Then (byte * byte)=word and then word/1000=55.
If you need a input like 350 which is a word and/or you want to use 2235/10000 then you will need to do word*word and word**word to get two words or 32 bits. You might also look at word*/word to get 16 bits out of the middle of the 32 bits.

[cncmachineguy]

Gee, and you question SO looked like you needed to multiply a whole number by .2235 and the .2235 was where the trouble is. If you need .00044*.2235, thats a different problem. You are correct, your question was simplified.Where are you getting numbers like .00044 in your pic? how is that generated?

[mark30504]

Gee, and you question SO looked like you needed to multiply a whole number by .2235 and the .2235 was where the trouble is. If you need .00044*.2235, thats a different problem. You are correct, your question was simplified.Where are you getting numbers like .00044 in your pic? how is that generated?

Hello

Thanks

I am just trying to understand the work around format in PIC to work with floating point values, the systems I normally program have floating point at part of there normal stucture.

I though from the orignal post that all you needed to do is use fractions in your formula and it would work but it does not seem to be so.

For example If I needed to multiply some varriable by .234 or any decimal value to get an answer, how would this be done?

In my case I am takeing a analog voltage and turning in into a tempature that is displayed on a screen.

The temperature result does not need to be floating point

But if I can not use floating point numbers to scale correctly the value could be off by 5+- degrees pretty quickly

The true formula is

result=adc10((adc10*.00034)+.2235) 'where adc10 in the pic 10 analog register

To be within 1% of the true tempature

Thanks

[Ioannis]

Yes, I always like the types of Stupid answer's one gets when asking a simple question.

Well, as was stated your question, ronsimpson did answer very good.

A simple thank would be OK if you did no liked the time he spent for you.

Anyway, PBP does not support FP directly. So tricks like the one suggested should be used.

A byte is 0-255 in range and a word 0-65535, so none will store you values as is.

Have a look at n-bit math here:

http://www.picbasic.co.uk/forum/show...ght=n-bit+math

or real Floating Point here:

http://melabs.com/resources/fp.htm

Ioannis

[mark30504]

Try to use DIV32.

Dummy VAR WORD
Number VAR BYTE
Result VAR BYTE
Dummy = Number * 1000
Result=DIV32 4474

Make sure I have this right.

By defineing Result at a byte, this will round the result to byte lenght ?

Lets say I need a decimal like .0004
Would I need several lines of code or can I just use

Dec1 VAR WORD
Result VAR BYTE
Something VAR WORD

Dec1=1/2500 'this should be .0004 ' will this work ? or need DIV32
Result = Something * Dec1 ' something being between 0 and 500

Result is now rounded ?

Do I alway need a DIV32 when a want a decimal result ?