flashforth-devel

Re: [Flashforth-devel] Floating point math for FF 5.x - IEEE-754 format

[om1zz <om...@vo...>]

This is a short intro how the single precision (32bit) floating point numbers work in the lib:

For example 3.141592653589793

converts into IEEE-754 single precision (32bit) floating point as:

0x40490FDA      as not rounded, or

0x40490FDB      as rounded.

That converts back to decimal format as:

0x40490FDA = 3.1415925  not rounded

0x40490FDB = 3.1415927 rounded.

So 32bit FP works with 7 decimal digits after the decimal point, 8 digits of mantissa (significand) in total are max what the IEEE-754 processes.

For an input the library can process 1 dec place of mantissa more (as the mantissa still fits into signed long int during processing the decimal string), therefore you may enter

f# 3.14159265e ( 314.159.265 fits ) and it will round properly into the binary FP format stored.

Entering additional digits of mantissa may not fit into signed long int (used during processing of the string) so it throws an overrun.

When printing with fs. (and the "precision" set to 7 - the number of ALL digits of mantissa to be printed out) you get

f# 3.14159265e fs. 3.141593E0   ok

When you want enter FP constants directly, you have to convert the decimal number into IEEE-754 single precision binary format and use (for example) as follows:

$0fda $4049 fconstant fpi
$0fda $c049 fconstant f-pi
$0fda $3fc9 fconstant fpi/2
$0fda $bfc9 fconstant f-pi/2

Mind the sequence - lower word first, then the higher word.

Or you may calculate directly with floats in hexa

$0fda $3fc9 $0fda $bfc9 f*           ( fpi/2  *  f-pi/2 )
f# 3.14159265e $0fda $3fc9 f/          ( fpi  /  fpi/2 )

Happy floating,
I.

[Flashforth-devel] Pick for Atmega

[Pablo M. M. <ea...@ho...>]

Hello,

I found that pick is no longer in core.txt. I suppose that the cause is that stack implementations change between proccesors, so now we need a different pick for each one. 

Just my humble contribution:

    \ xu ... x0 u -- xu ... x0 xu
    : pick 2* sp@ + @ ;

Tested with FF5.0 on an ATmega328p. 

73, Pablo - EA4FUK
 		 	   		  

Re: [Flashforth-devel] Pick for Atmega

[Mikael N. <mik...@fl...>]

Thanks.
I will add it to the distribution.

BR Mike

On 17.05.2015 14:23, Pablo M. Muñoz wrote:
> Hello,
>
> I found that pick is no longer in core.txt. I suppose that the cause is
> that stack implementations change between proccesors, so now we need a
> different pick for each one.
>
> Just my humble contribution:
>
>      \ xu ... x0 u -- xu ... x0 xu
>      : pick 2* sp@ + @ ;
>
> Tested with FF5.0 on an ATmega328p.
>
> 73, Pablo - EA4FUK
>

Re: [Flashforth-devel] Floating point math for FF 5.x - IEEE-754 format - Part II.

[om1zz <om...@vo...>]

Part II.
This is a short intro how the single precision (32bit) floating point numbers work in the lib:

We need to process some data coming from ADC, 9DOF, I2C sensors with our FF system, of course :)

To process integers you may use the s>f and d>f words for conversion to float.

For example, with "precison" set to 7 (6decimal places) for printing with fs. :

16bit signed integers:

100 s>f fs. 1.000000E2  ok<#,ram>
-100 s>f fs. -1.000000E2  ok<#,ram>

30001 s>f fs. 3.000100E4  ok<#,ram>
-30001 s>f fs. -3.000100E4  ok<#,ram>

32bit signed integers:

12000000. d>f fs. 1.200000E7  ok<#,ram>
-12000000. d>f fs. -1.200000E7  ok<#,ram>

12345678. d>f fs. 1.234568E7  ok<#,ram>

10000000. d>f 10000000. d>f f* fs. 1.000000E14  ok<#,ram>

-1000000. d>f 1. d>f f+ fs. -9.999990E5  ok<#,ram>


Happy floating!
I.