Difference: FloatingPointUnit (10 vs. 11)

Revision 112022-11-02 - PeterSchmid

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Intro

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Why Floating Point?

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Why Floating-Point?

STM AN4044: One alternative to floating-point is fixed-point, where the exponent field is fixed. But if fixed-point is giving better calculation speed on FPU-less processors, the range of numbers and their dynamic is low. As a consequence, a developer using the fixed-point technique will have to check carefully any scaling/saturation issues in the algorithm.

Coding	Dynamic [dB]
Int32	192
Int64	385
Single precision	1529
Double precision	12318

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< Forth systems traditionally make use of cooperative multitasking. It is very simple and clever. But it has its limits. If you write all your software by yourself, each software part can be cooperative. But if you want to benefit from middleware written by somebody else (and most probably not written in Forth), you can be sure that software is not cooperative (in the context of multitasking). Forth wants to rule your system. I would like to have a Forth system that is cooperative. It should extend the system, to make it interactive and easy to use.

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< The Forth interpreter (called terminal task in Forth jargon) itself is only a thread and can be used as some sort of CLI for testing purposes or could be the main part of the application.

Contents

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Forth Multitasking

Andrew Haley wrote "Forth has been multi-tasking for almost 50 years. It's time to standardize it" and he is right. I will implement his proposed API for Mecrisp-Cube described in A multi-tasking wordset for Standard Forth

. The multitasker wordset is very similar to the one in SwiftForth / PolyForth.

I use the term task here because it is well known in the Forth world, although Mecrisp-Cube make use of threads. Mecrisp-Cube tasks are CMSIS-RTOS threads with user variables. The Mecrisp-Cube (CMSIS-RTOS / FreeRTOS) scheduler is pre-emptive and not round robin (cooperative). Mecrisp-Cube is always multi tasked, you can not switch off the scheduler and therefore there is no MULTI, SINGLE, or INIT-MULTI.

Floating Point Unit

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Floating-Point Unit

Fixed Point

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Floating Point Words

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Floating-Point Words

Bare FPU Words (Without C Math Library)

f+      ( r1 r2 -- r3 )     Add r1 to r2 giving the sum r3.

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fabs ( r1 -- r2 ) r2 is the absolute value of r1. fnegate ( r1 -- r2 ) r2 is the negation of r1.

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> f0= ( r -- ? ) flag is true if and only if r is equal to zero f0< ( r -- ? ) flag is true if and only if r is less than zero f< ( r1 r2 -- ? ) flag is true if and only if r1 is less than r2 f~ ( r1 r2 r3 -- ? ) If r3 is positive, flag is true if the absolute value of (r1 minus r2) is less than r3 If r3 is zero, flag is true if the implementation-dependent encoding of r1 and r2 are exactly identical (positive and negative zero are unequal if they have distinct encodings). If r3 is negative, flag is true if the absolute value of (r1 minus r2) is less than the absolute value of r3 times the sum of the absolute values of r1 and r2.

f>s ( r -- n ) n is the single-cell signed-integer equivalent of the integer portion of r. s>f ( n -- r ) r is the floating-point equivalent of the single-cell value n. f>fx ( r -- d ) d is the fixed-point equivalent of the floating-point r

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f. ( r -- ) Display, with a trailing space, the top number using fixed-point notation:

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> fx* fx/

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C Math Library

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Words Using C Math Library

fsin    ( r1 -- r2 )       r2 is the sine of the radian angle r1

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