Glossary

Imm

An immediate value (or simply an immediate or imm) is a piece of data that is stored as part of the instruction itself instead of being in a memory location or a register. Immediate values are typically used in instructions that load a value or performs an arithmetic or a logical operation on a constant.

ARM data processing instructions have 12 bits of space for values in their instruction word. This is arranged as a four-bit rotate value and an eight-bit immediate value.

The 4-bit rotate value stored in bits 11-8 is multiplied by two giving a range of 0-30 in steps of two.

Using this scheme we can express immediate constants such as:

0x000000FF
0x00000FF0
0xFF000000
0xF000000F

But immediate constants such as:

0x000001FE
0xF000F000
0x55550000

…are not possible.

An assembler will convert big values to the rotated form. Impossible values will cause an error.

Some assemblers will use other tricks such as using MVN instead of MOV to form the bitwise complement of the required constant. For example the impossible instruction MOV r0,#0xFFFFFFFF could be assembled as MVN r0,#0.

REF: DaveSpace

<builds does>

Or create does>

Michael Ham has called the word pair CREATE...DOES>, the “pearl of Forth”. CREATE is a component of the compiler, whose function is to make a new dictionary entry with a given name (the next name in the input stream) and nothing else. DOES> assigns a specific run-time action to a newly CREATEd word.

Folding

Constant folding is a well known technique in optimisation. It means that if an operator works on constants the result may be replaced by a constant that is calculated at compile time. In Forth we generalise this to folding. Folding refers to all words that can be replaced by simpler words in case they receive constant data on the stack. REF: a.w.m.van.der.horst

Inlining

Inlining means replacing a Forth word with its constituents. This technique is very important in Forth, more so than in other languages, due to the small size of Forth words. Inlining is always a winner in speed, and mostly even also a winner with regard to space.

Even more important is the fact that inlining allows folding to be applied across constituent words. This applies to high level and low level code alike.

Inlining high level code is trivial. A further inlining stage replaces a high level definition that only calls code words, by a code definition which concatenates the code words. REF: a.w.m.van.der.horst

Smudge

Finishes a definition by flushing all flash buffers and inserts a link into the dictionary chain, making the new definition visible.

Vocabularies

July 2017, great news! Manfred Mahlow’s Final Release of VOCs extension for Mecrisp-Stellaris 2.3.6-hook-find (vocs-0.6.2-FR) has arrived for testing. See the new GPIO MODE Demo

Amforth

In amforth there is a word that can place newly defined words in wordlists automatically. e.g. a word called foo:bar is placed as bar in wordlist foo. It is like a sibling of a dot (colon)-recognizer that can detect the foo:bar notation and searches bar in foo (only). This word does not affect the definition wordlist or the search order, not even temporarily. REF: Mathias Trute

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