This is Info file gforth.info, produced by Makeinfo version 1.68 from
the input file gforth.texi.

INFO-DIR-SECTION GNU programming tools
START-INFO-DIR-ENTRY
* Gforth: (gforth).             A fast interpreter for the Forth language.
END-INFO-DIR-ENTRY

   This file documents Gforth 0.4.0

   Copyright (C) 1995-1998 Free Software Foundation, Inc.

   Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
 are preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this      manual under the conditions for verbatim copying, provided
also that the      sections entitled "Distribution" and "General Public
License" are      included exactly as in the original, and provided
that the entire      resulting derived work is distributed under the
terms of a permission      notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual      into another language, under the above conditions for
modified versions,      except that the sections entitled
"Distribution" and "General Public      License" may be included in a
translation approved by the author instead      of in the original
English.


File: gforth.info,  Node: Top,  Next: License,  Prev: (dir),  Up: (dir)

   Gforth is a free implementation of ANS Forth available on many
personal machines. This manual corresponds to version 0.4.0.

* Menu:

* License::
* Goals::                       About the Gforth Project
* Other Books::                 Things you might want to read
* Invoking Gforth::             Starting Gforth
* Words::                       Forth words available in Gforth
* Tools::                       Programming tools
* ANS conformance::             Implementation-defined options etc.
* Model::                       The abstract machine of Gforth
* Integrating Gforth::          Forth as scripting language for applications
* Emacs and Gforth::            The Gforth Mode
* Image Files::                 `.fi' files contain compiled code
* Engine::                      The inner interpreter and the primitives
* Cross Compiler::              The Cross Compiler
* Bugs::                        How to report them
* Origin::                      Authors and ancestors of Gforth
* Word Index::                  An item for each Forth word
* Concept Index::               A menu covering many topics

 -- The Detailed Node Listing --

Forth Words

* Notation::
* Arithmetic::
* Stack Manipulation::
* Memory::
* Control Structures::
* Locals::
* Defining Words::
* Structures::
* Object-oriented Forth::
* Tokens for Words::
* Wordlists::
* Files::
* Including Files::
* Blocks::
* Other I/O::
* Programming Tools::
* Assembler and Code Words::
* Threading Words::

Arithmetic

* Single precision::
* Bitwise operations::
* Mixed precision::             operations with single and double-cell integers
* Double precision::            Double-cell integer arithmetic
* Floating Point::

Stack Manipulation

* Data stack::
* Floating point stack::
* Return stack::
* Locals stack::
* Stack pointer manipulation::

Memory

* Memory Access::
* Address arithmetic::
* Memory Blocks::

Control Structures

* Selection::
* Simple Loops::
* Counted Loops::
* Arbitrary control structures::
* Calls and returns::
* Exception Handling::

Locals

* Gforth locals::
* ANS Forth locals::

Gforth locals

* Where are locals visible by name?::
* How long do locals live?::
* Programming Style::
* Implementation::

Defining Words

* Simple Defining Words::
* Colon Definitions::
* User-defined Defining Words::
* Supplying names::
* Interpretation and Compilation Semantics::

Structures

* Why explicit structure support?::
* Structure Usage::
* Structure Naming Convention::
* Structure Implementation::
* Structure Glossary::

Object-oriented Forth

* Objects::
* OOF::
* Mini-OOF::

Objects

* Properties of the Objects model::
* Why object-oriented programming?::
* Object-Oriented Terminology::
* Basic Objects Usage::
* The class Object::
* Creating objects::
* Object-Oriented Programming Style::
* Class Binding::
* Method conveniences::
* Classes and Scoping::
* Object Interfaces::
* Objects Implementation::
* Comparison with other object models::
* Objects Glossary::

OOF

* Properties of the OOF model::
* Basic OOF Usage::
* The base class object::
* Class Declaration::
* Class Implementation::

Including Files

* Words for Including::
* Search Path::
* Changing the Search Path::
* General Search Paths::

Programming Tools

* Debugging::                   Simple and quick.
* Assertions::                  Making your programs self-checking.
* Singlestep Debugger::		Executing your program word by word.

Tools

* ANS Report::                  Report the words used, sorted by wordset.

ANS conformance

* The Core Words::
* The optional Block word set::
* The optional Double Number word set::
* The optional Exception word set::
* The optional Facility word set::
* The optional File-Access word set::
* The optional Floating-Point word set::
* The optional Locals word set::
* The optional Memory-Allocation word set::
* The optional Programming-Tools word set::
* The optional Search-Order word set::

The Core Words

* core-idef::                   Implementation Defined Options
* core-ambcond::                Ambiguous Conditions
* core-other::                  Other System Documentation

The optional Block word set

* block-idef::                  Implementation Defined Options
* block-ambcond::               Ambiguous Conditions
* block-other::                 Other System Documentation

The optional Double Number word set

* double-ambcond::              Ambiguous Conditions

The optional Exception word set

* exception-idef::              Implementation Defined Options

The optional Facility word set

* facility-idef::               Implementation Defined Options
* facility-ambcond::            Ambiguous Conditions

The optional File-Access word set

* file-idef::                   Implementation Defined Options
* file-ambcond::                Ambiguous Conditions

The optional Floating-Point word set

* floating-idef::               Implementation Defined Options
* floating-ambcond::            Ambiguous Conditions

The optional Locals word set

* locals-idef::                 Implementation Defined Options
* locals-ambcond::              Ambiguous Conditions

The optional Memory-Allocation word set

* memory-idef::                 Implementation Defined Options

The optional Programming-Tools word set

* programming-idef::            Implementation Defined Options
* programming-ambcond::         Ambiguous Conditions

The optional Search-Order word set

* search-idef::                 Implementation Defined Options
* search-ambcond::              Ambiguous Conditions

Image Files

* Image File Background::          Why have image files?
* Non-Relocatable Image Files::    don't always work.
* Data-Relocatable Image Files::   are better.
* Fully Relocatable Image Files::  better yet.
* Stack and Dictionary Sizes::     Setting the default sizes for an image.
* Running Image Files::            `gforth -i FILE' or FILE.
* Modifying the Startup Sequence:: and turnkey applications.

Fully Relocatable Image Files

* gforthmi::            The normal way
* cross.fs::                    The hard way

Engine

* Portability::
* Threading::
* Primitives::
* Performance::

Threading

* Scheduling::
* Direct or Indirect Threaded?::
* DOES>::

Primitives

* Automatic Generation::
* TOS Optimization::
* Produced code::

System Libraries

* Binding to System Library::

Cross Compiler

* Using the Cross Compiler::
* How the Cross Compiler Works::


File: gforth.info,  Node: License,  Next: Goals,  Prev: Top,  Up: Top

GNU GENERAL PUBLIC LICENSE
**************************

                         Version 2, June 1991

     Copyright (C) 1989, 1991 Free Software Foundation, Inc.
     675 Mass Ave, Cambridge, MA 02139, USA
     
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

Preamble
========

   The licenses for most software are designed to take away your
freedom to share and change it.  By contrast, the GNU General Public
License is intended to guarantee your freedom to share and change free
software--to make sure the software is free for all its users.  This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it.  (Some other Free Software Foundation software is covered by
the GNU Library General Public License instead.)  You can apply it to
your programs, too.

   When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
this service if you wish), that you receive source code or can get it
if you want it, that you can change the software or use pieces of it in
new free programs; and that you know you can do these things.

   To protect your rights, we need to make restrictions that forbid
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These restrictions translate to certain responsibilities for you if you
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   For example, if you distribute copies of such a program, whether
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you have.  You must make sure that they, too, receive or can get the
source code.  And you must show them these terms so they know their
rights.

   We protect your rights with two steps: (1) copyright the software,
and (2) offer you this license which gives you legal permission to copy,
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   Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
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   Finally, any free program is threatened constantly by software
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   The precise terms and conditions for copying, distribution and
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    TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  0. This License applies to any program or other work which contains a
     notice placed by the copyright holder saying it may be distributed
     under the terms of this General Public License.  The "Program",
     below, refers to any such program or work, and a "work based on
     the Program" means either the Program or any derivative work under
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     licensee is addressed as "you".

     Activities other than copying, distribution and modification are
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     Program is covered only if its contents constitute a work based on
     the Program (independent of having been made by running the
     Program).  Whether that is true depends on what the Program does.

  1. You may copy and distribute verbatim copies of the Program's
     source code as you receive it, in any medium, provided that you
     conspicuously and appropriately publish on each copy an appropriate
     copyright notice and disclaimer of warranty; keep intact all the
     notices that refer to this License and to the absence of any
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     this License along with the Program.

     You may charge a fee for the physical act of transferring a copy,
     and you may at your option offer warranty protection in exchange
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       a. You must cause the modified files to carry prominent notices
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       b. You must cause any work that you distribute or publish, that
          in whole or in part contains or is derived from the Program
          or any part thereof, to be licensed as a whole at no charge
          to all third parties under the terms of this License.

       c. If the modified program normally reads commands interactively
          when run, you must cause it, when started running for such
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          an announcement including an appropriate copyright notice and
          a notice that there is no warranty (or else, saying that you
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          to print an announcement.)

     These requirements apply to the modified work as a whole.  If
     identifiable sections of that work are not derived from the
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     apply to those sections when you distribute them as separate
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     whole which is a work based on the Program, the distribution of
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     for other licensees extend to the entire whole, and thus to each
     and every part regardless of who wrote it.

     Thus, it is not the intent of this section to claim rights or
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     In addition, mere aggregation of another work not based on the
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  3. You may copy and distribute the Program (or a work based on it,
     under Section 2) in object code or executable form under the terms
     of Sections 1 and 2 above provided that you also do one of the
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       a. Accompany it with the complete corresponding machine-readable
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     The source code for a work means the preferred form of the work for
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  4. You may not copy, modify, sublicense, or distribute the Program
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     royalty-free redistribution of the Program by all those who
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     entirely from distribution of the Program.

     If any portion of this section is held invalid or unenforceable
     under any particular circumstance, the balance of the section is
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     any such claims; this section has the sole purpose of protecting
     the integrity of the free software distribution system, which is
     implemented by public license practices.  Many people have made
     generous contributions to the wide range of software distributed
     through that system in reliance on consistent application of that
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  9. The Free Software Foundation may publish revised and/or new
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 10. If you wish to incorporate parts of the Program into other free
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                                NO WARRANTY

 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO
     WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE
     LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
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 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
     WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY
     MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE
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     OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN
     ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

                      END OF TERMS AND CONDITIONS

How to Apply These Terms to Your New Programs
=============================================

   If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

   To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
     Copyright (C) 19YY  NAME OF AUTHOR
     
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 2 of the License, or
     (at your option) any later version.
     
     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.
     
     You should have received a copy of the GNU General Public License
     along with this program; if not, write to the Free Software
     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

   Also add information on how to contact you by electronic and paper
mail.

   If the program is interactive, make it output a short notice like
this when it starts in an interactive mode:

     Gnomovision version 69, Copyright (C) 19YY NAME OF AUTHOR
     Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
     type `show w'.
     This is free software, and you are welcome to redistribute it
     under certain conditions; type `show c' for details.

   The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License.  Of course, the
commands you use may be called something other than `show w' and `show
c'; they could even be mouse-clicks or menu items--whatever suits your
program.

   You should also get your employer (if you work as a programmer) or
your school, if any, to sign a "copyright disclaimer" for the program,
if necessary.  Here is a sample; alter the names:

     Yoyodyne, Inc., hereby disclaims all copyright interest in the program
     `Gnomovision' (which makes passes at compilers) written by James Hacker.
     
     SIGNATURE OF TY COON, 1 April 1989
     Ty Coon, President of Vice

   This General Public License does not permit incorporating your
program into proprietary programs.  If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library.  If this is what you want to do, use the
GNU Library General Public License instead of this License.


File: gforth.info,  Node: Goals,  Next: Other Books,  Prev: License,  Up: Top

Goals of Gforth
***************

   The goal of the Gforth Project is to develop a standard model for
ANS Forth. This can be split into several subgoals:

   * Gforth should conform to the Forth standard (ANS Forth).

   * It should be a model, i.e. it should define all the
     implementation-dependent things.

   * It should become standard, i.e. widely accepted and used. This goal
     is the most difficult one.

   To achieve these goals Gforth should be
   * Similar to previous models (fig-Forth, F83)

   * Powerful. It should provide for all the things that are considered
     necessary today and even some that are not yet considered
     necessary.

   * Efficient. It should not get the reputation of being exceptionally
     slow.

   * Free.

   * Available on many machines/easy to port.

   Have we achieved these goals? Gforth conforms to the ANS Forth
standard. It may be considered a model, but we have not yet documented
which parts of the model are stable and which parts we are likely to
change. It certainly has not yet become a de facto standard, but it
appears to be quite popular. It has some similarities to and some
differences from previous models. It has some powerful features, but not
yet everything that we envisioned. We certainly have achieved our
execution speed goals (*note Performance::.).  It is free and available
on many machines.


File: gforth.info,  Node: Other Books,  Next: Invoking Gforth,  Prev: Goals,  Up: Top

Other books on ANS Forth
************************

   As the standard is relatively new, there are not many books out yet.
It is not recommended to learn Forth by using Gforth and a book that is
not written for ANS Forth, as you will not know your mistakes from the
deviations of the book. However, books based on the Forth-83 standard
should be ok, because ANS Forth is primarily an extension of Forth-83.

   There is, of course, the standard, the definite reference if you
want to write ANS Forth programs. It is available in printed form from
the National Standards Institute Sales Department (Tel.: USA (212)
642-4900; Fax.: USA (212) 302-1286) as document `X3.215-1994' for about
$200. You can also get it from Global Engineering Documents (Tel.: USA
(800) 854-7179; Fax.: (303) 843-9880) for about $300.

   `dpANS6', the last draft of the standard, which was then submitted
to ANSI for publication is available electronically and for free in some
MS Word format, and it has been converted to HTML
(`http://www.taygeta.com/forth/dpans.html'; this is my favourite
format); this HTML version also includes the answers to Requests for
Interpretation (RFIs). Some pointers to these versions can be found
through
`http://www.complang.tuwien.ac.at/projects/forth.html'.

   `Forth: The New Model' by Jack Woehr (Prentice-Hall, 1993) is an
introductory book based on a draft version of the standard. It does not
cover the whole standard. It also contains interesting background
information (Jack Woehr was in the ANS Forth Technical Committee). It is
not appropriate for complete newbies, but programmers experienced in
other languages should find it ok.

   `Forth Programmer's Handbook' by Edward K. Conklin, Elizabeth D.
Rather and the technical staff of Forth, Inc. (Forth, Inc., 1997; ISBN
0-9662156-0-5) contains little introductory material. The majority of
the book is similar to *Note Words::, but the book covers most of the
standard words and some non-standard words (whereas this manual is
quite incomplete). In addition, the book contains a chapter on
programming style. The major drawback of this book is that it usually
does not identify what is standard and what is specific to the Forth
system described in the book (probably one of Forth, Inc.'s systems).
Fortunately, many of the non-standard programming practices described in
the book work in Gforth, too.  Still, this drawback makes the book
hardly more useful than a pre-ANS book.


File: gforth.info,  Node: Invoking Gforth,  Next: Words,  Prev: Other Books,  Up: Top

Invoking Gforth
***************

   You will usually just say `gforth'. In many other cases the default
Gforth image will be invoked like this:
     gforth [files] [-e forth-code]
   This interprets the contents of the files and the Forth code in the
order they are given.

   In general, the command line looks like this:

     gforth [initialization options] [image-specific options]

   The initialization options must come before the rest of the command
line. They are:

`--image-file FILE'
`-i FILE'
     Loads the Forth image FILE instead of the default `gforth.fi'
     (*note Image Files::.).

`--path PATH'
`-p PATH'
     Uses PATH for searching the image file and Forth source code files
     instead of the default in the environment variable `GFORTHPATH' or
     the path specified at installation time (e.g.,
     `/usr/local/share/gforth/0.2.0:.'). A path is given as a list of
     directories, separated by `:' (on Unix) or `;' (on other OSs).

`--dictionary-size SIZE'
`-m SIZE'
     Allocate SIZE space for the Forth dictionary space instead of
     using the default specified in the image (typically 256K). The
     SIZE specification consists of an integer and a unit (e.g., `4M').
     The unit can be one of `b' (bytes), `e' (element size, in this
     case Cells), `k' (kilobytes), `M' (Megabytes), `G' (Gigabytes),
     and `T' (Terabytes). If no unit is specified, `e' is used.

`--data-stack-size SIZE'
`-d SIZE'
     Allocate SIZE space for the data stack instead of using the
     default specified in the image (typically 16K).

`--return-stack-size SIZE'
`-r SIZE'
     Allocate SIZE space for the return stack instead of using the
     default specified in the image (typically 15K).

`--fp-stack-size SIZE'
`-f SIZE'
     Allocate SIZE space for the floating point stack instead of using
     the default specified in the image (typically 15.5K). In this case
     the unit specifier `e' refers to floating point numbers.

`--locals-stack-size SIZE'
`-l SIZE'
     Allocate SIZE space for the locals stack instead of using the
     default specified in the image (typically 14.5K).

`--help'
`-h'
     Print a message about the command-line options

`--version'
`-v'
     Print version and exit

`--debug'
     Print some information useful for debugging on startup.

`--offset-image'
     Start the dictionary at a slightly different position than would
     be used otherwise (useful for creating data-relocatable images,
     *note Data-Relocatable Image Files::.).

`--no-offset-im'
     Start the dictionary at the normal position.

`--clear-dictionary'
     Initialize all bytes in the dictionary to 0 before loading the
     image (*note Data-Relocatable Image Files::.).

`--die-on-signal'
     Normally Gforth handles most signals (e.g., the user interrupt
     SIGINT, or the segmentation violation SIGSEGV) by translating it
     into a Forth `THROW'. With this option, Gforth exits if it
     receives such a signal. This option is useful when the engine
     and/or the image might be severely broken (such that it causes
     another signal before recovering from the first); this option
     avoids endless loops in such cases.

   As explained above, the image-specific command-line arguments for the
default image `gforth.fi' consist of a sequence of filenames and `-e
FORTH-CODE' options that are interpreted in the sequence in which they
are given. The `-e FORTH-CODE' or `--evaluate FORTH-CODE' option
evaluates the forth code. This option takes only one argument; if you
want to evaluate more Forth words, you have to quote them or use
several `-e's. To exit after processing the command line (instead of
entering interactive mode) append `-e bye' to the command line.

   If you have several versions of Gforth installed, `gforth' will
invoke the version that was installed last. `gforth-VERSION' invokes a
specific version. You may want to use the option `--path', if your
environment contains the variable `GFORTHPATH'.

   Not yet implemented: On startup the system first executes the system
initialization file (unless the option `--no-init-file' is given; note
that the system resulting from using this option may not be ANS Forth
conformant). Then the user initialization file `.gforth.fs' is
executed, unless the option `--no-rc' is given; this file is first
searched in `.', then in `~', then in the normal path (see above).


File: gforth.info,  Node: Words,  Next: Tools,  Prev: Invoking Gforth,  Up: Top

Forth Words
***********

* Menu:

* Notation::
* Arithmetic::
* Stack Manipulation::
* Memory::
* Control Structures::
* Locals::
* Defining Words::
* Structures::
* Object-oriented Forth::
* Tokens for Words::
* Wordlists::
* Files::
* Including Files::
* Blocks::
* Other I/O::
* Programming Tools::
* Assembler and Code Words::
* Threading Words::


File: gforth.info,  Node: Notation,  Next: Arithmetic,  Prev: Words,  Up: Words

Notation
========

   The Forth words are described in this section in the glossary
notation that has become a de-facto standard for Forth texts, i.e.,

WORD     STACK EFFECT   WORDSET   PRONUNCIATION
   DESCRIPTION

WORD
     The name of the word. BTW, Gforth is case insensitive, so you can
     type the words in in lower case (However, *note core-idef::.).

STACK EFFECT
     The stack effect is written in the notation `BEFORE -- AFTER',
     where BEFORE and AFTER describe the top of stack entries before
     and after the execution of the word. The rest of the stack is not
     touched by the word. The top of stack is rightmost, i.e., a stack
     sequence is written as it is typed in. Note that Gforth uses a
     separate floating point stack, but a unified stack notation. Also,
     return stack effects are not shown in STACK EFFECT, but in
     DESCRIPTION. The name of a stack item describes the type and/or
     the function of the item. See below for a discussion of the types.

     All words have two stack effects: A compile-time stack effect and a
     run-time stack effect. The compile-time stack-effect of most words
     is  - . If the compile-time stack-effect of a word deviates from
     this standard behaviour, or the word does other unusual things at
     compile time, both stack effects are shown; otherwise only the
     run-time stack effect is shown.

PRONUNCIATION
     How the word is pronounced.

WORDSET
     The ANS Forth standard is divided into several wordsets. A standard
     system need not support all of them. So, the fewer wordsets your
     program uses the more portable it will be in theory. However, we
     suspect that most ANS Forth systems on personal machines will
     feature all wordsets. Words that are not defined in the ANS
     standard have `gforth' or `gforth-internal' as wordset. `gforth'
     describes words that will work in future releases of Gforth;
     `gforth-internal' words are more volatile. Environmental query
     strings are also displayed like words; you can recognize them by
     the `environment' in the wordset field.

DESCRIPTION
     A description of the behaviour of the word.

   The type of a stack item is specified by the character(s) the name
starts with:

`f'
     Boolean flags, i.e. `false' or `true'.

`c'
     Char

`w'
     Cell, can contain an integer or an address

`n'
     signed integer

`u'
     unsigned integer

`d'
     double sized signed integer

`ud'
     double sized unsigned integer

`r'
     Float (on the FP stack)

`a_'
     Cell-aligned address

`c_'
     Char-aligned address (note that a Char may have two bytes in
     Windows NT)

`f_'
     Float-aligned address

`df_'
     Address aligned for IEEE double precision float

`sf_'
     Address aligned for IEEE single precision float

`xt'
     Execution token, same size as Cell

`wid'
     Wordlist ID, same size as Cell

`f83name'
     Pointer to a name structure

`"'
     string in the input stream (not on the stack). The terminating
     character is a blank by default. If it is not a blank, it is shown
     in `<>' quotes.


File: gforth.info,  Node: Arithmetic,  Next: Stack Manipulation,  Prev: Notation,  Up: Words

Arithmetic
==========

   Forth arithmetic is not checked, i.e., you will not hear about
integer overflow on addition or multiplication, you may hear about
division by zero if you are lucky. The operator is written after the
operands, but the operands are still in the original order. I.e., the
infix `2-1' corresponds to `2 1 -'. Forth offers a variety of division
operators. If you perform division with potentially negative operands,
you do not want to use `/' or `/mod' with its undefined behaviour, but
rather `fm/mod' or `sm/mod' (probably the former, *note Mixed
precision::.).

* Menu:

* Single precision::
* Bitwise operations::
* Mixed precision::             operations with single and double-cell integers
* Double precision::            Double-cell integer arithmetic
* Floating Point::


File: gforth.info,  Node: Single precision,  Next: Bitwise operations,  Prev: Arithmetic,  Up: Arithmetic

Single precision
----------------

`+'       n1 n2 - n       core       ``plus''

`-'       n1 n2 - n       core       ``minus''

`*'       n1 n2 - n       core       ``star''

`/'       n1 n2 - n       core       ``slash''

`mod'       n1 n2 - n       core       ``mod''

`/mod'       n1 n2 - n3 n4       core       ``slash-mod''

`negate'       n1 - n2       core       ``negate''

`abs'       n1 - n2       core       ``abs''

`min'       n1 n2 - n       core       ``min''

`max'       n1 n2 - n       core       ``max''


File: gforth.info,  Node: Bitwise operations,  Next: Mixed precision,  Prev: Single precision,  Up: Arithmetic

Bitwise operations
------------------

`and'       w1 w2 - w       core       ``and''

`or'       w1 w2 - w       core       ``or''

`xor'       w1 w2 - w       core       ``xor''

`invert'       w1 - w2       core       ``invert''

`2*'       n1 - n2       core       ``two-star''

`2/'       n1 - n2       core       ``two-slash''


File: gforth.info,  Node: Mixed precision,  Next: Double precision,  Prev: Bitwise operations,  Up: Arithmetic

Mixed precision
---------------

`m+'       d1 n - d2       double       ``m-plus''

`*/'       n1 n2 n3 - n4         core       ``star-slash''

`*/mod'       n1 n2 n3 - n4 n5         core       ``star-slash-mod''

`m*'       n1 n2 - d       core       ``m-star''

`um*'       u1 u2 - ud       core       ``u-m-star''

`m*/'       d1 n2 u3 - dqout         double       ``m-star-slash''

`um/mod'       ud u1 - u2 u3       core       ``u-m-slash-mod''

`fm/mod'       d1 n1 - n2 n3       core       ``f-m-slash-mod''
   floored division: d1 = n3*n1+n2, n1>n2>=0 or 0>=n2>n1

`sm/rem'       d1 n1 - n2 n3       core       ``s-m-slash-rem''
   symmetric division: d1 = n3*n1+n2, sign(n2)=sign(d1) or 0


File: gforth.info,  Node: Double precision,  Next: Floating Point,  Prev: Mixed precision,  Up: Arithmetic

Double precision
----------------

   The outer (aka text) interpreter converts numbers containing a dot
into a double precision number. Note that only numbers with the dot as
last character are standard-conforming.

`d+'       d1 d2 - d       double       ``d-plus''

`d-'       d1 d2 - d       double       ``d-minus''

`dnegate'       d1 - d2       double       ``dnegate''

`dabs'       d1 - d2         double       ``dabs''

`dmin'       d1 d2 - d         double       ``dmin''

`dmax'       d1 d2 - d         double       ``dmax''


File: gforth.info,  Node: Floating Point,  Prev: Double precision,  Up: Arithmetic

Floating Point
--------------

   The format of floating point numbers recognized by the outer (aka
text) interpreter is: a signed decimal number, possibly containing a
decimal point (`.'), followed by `E' or `e', optionally followed by a
signed integer (the exponent). E.g., `1e' is the same as `+1.0e+0'.
Note that a number without `e' is not interpreted as floating-point
number, but as double (if the number contains a `.') or single
precision integer. Also, conversions between string and floating point
numbers always use base 10, irrespective of the value of `BASE' (in
Gforth; for the standard this is an ambiguous condition). If `BASE'
contains a value greater then 14, the `E' may be interpreted as digit
and the number will be interpreted as integer, unless it has a signed
exponent (both `+' and `-' are allowed as signs).

   Angles in floating point operations are given in radians (a full
circle has 2 pi radians). Note, that Gforth has a separate floating
point stack, but we use the unified notation.

   Floating point numbers have a number of unpleasant surprises for the
unwary (e.g., floating point addition is not associative) and even a few
for the wary. You should not use them unless you know what you are doing
or you don't care that the results you get are totally bogus. If you
want to learn about the problems of floating point numbers (and how to
avoid them), you might start with `David Goldberg, What Every Computer
Scientist Should Know About Floating-Point Arithmetic, ACM Computing
Surveys 23(1):5-48, March 1991'
(`http://www.validgh.com/goldberg/paper.ps').

`f+'       r1 r2 - r3       float       ``f-plus''

`f-'       r1 r2 - r3       float       ``f-minus''

`f*'       r1 r2 - r3       float       ``f-star''

`f/'       r1 r2 - r3       float       ``f-slash''

`fnegate'       r1 - r2       float       ``fnegate''

`fabs'       r1 - r2       float-ext       ``fabs''

`fmax'       r1 r2 - r3       float       ``fmax''

`fmin'       r1 r2 - r3       float       ``fmin''

`floor'       r1 - r2       float       ``floor''
   round towards the next smaller integral value, i.e., round toward
negative infinity

`fround'       r1 - r2       float       ``fround''
   round to the nearest integral value

`f**'       r1 r2 - r3       float-ext       ``f-star-star''
   r3 is r1 raised to the r2th power

`fsqrt'       r1 - r2       float-ext       ``fsqrt''

`fexp'       r1 - r2       float-ext       ``fexp''

`fexpm1'       r1 - r2       float-ext       ``fexpm1''
   r2=e**r1-1

`fln'       r1 - r2       float-ext       ``fln''

`flnp1'       r1 - r2       float-ext       ``flnp1''
   r2=ln(r1+1)

`flog'       r1 - r2       float-ext       ``flog''
   the decimal logarithm

`falog'       r1 - r2       float-ext       ``falog''
   r2=10**r1

`fsin'       r1 - r2       float-ext       ``fsin''

`fcos'       r1 - r2       float-ext       ``fcos''

`fsincos'       r1 - r2 r3       float-ext       ``fsincos''
   r2=sin(r1), r3=cos(r1)

`ftan'       r1 - r2       float-ext       ``ftan''

`fasin'       r1 - r2       float-ext       ``fasin''

`facos'       r1 - r2       float-ext       ``facos''

`fatan'       r1 - r2       float-ext       ``fatan''

`fatan2'       r1 r2 - r3       float-ext       ``fatan2''
   r1/r2=tanr3. The standard does not require, but probably intends
this to be the inverse of `fsincos'. In gforth it is.

`fsinh'       r1 - r2       float-ext       ``fsinh''

`fcosh'       r1 - r2       float-ext       ``fcosh''

`ftanh'       r1 - r2       float-ext       ``ftanh''

`fasinh'       r1 - r2       float-ext       ``fasinh''

`facosh'       r1 - r2       float-ext       ``facosh''

`fatanh'       r1 - r2       float-ext       ``fatanh''


File: gforth.info,  Node: Stack Manipulation,  Next: Memory,  Prev: Arithmetic,  Up: Words

Stack Manipulation
==================

   Gforth has a data stack (aka parameter stack) for characters, cells,
addresses, and double cells, a floating point stack for floating point
numbers, a return stack for storing the return addresses of colon
definitions and other data, and a locals stack for storing local
variables. Note that while every sane Forth has a separate floating
point stack, this is not strictly required; an ANS Forth system could
theoretically keep floating point numbers on the data stack. As an
additional difficulty, you don't know how many cells a floating point
number takes. It is reportedly possible to write words in a way that
they work also for a unified stack model, but we do not recommend trying
it. Instead, just say that your program has an environmental dependency
on a separate FP stack.

   Also, a Forth system is allowed to keep the local variables on the
return stack. This is reasonable, as local variables usually eliminate
the need to use the return stack explicitly. So, if you want to produce
a standard complying program and if you are using local variables in a
word, forget about return stack manipulations in that word (see the
standard document for the exact rules).

* Menu:

* Data stack::
* Floating point stack::
* Return stack::
* Locals stack::
* Stack pointer manipulation::


File: gforth.info,  Node: Data stack,  Next: Floating point stack,  Prev: Stack Manipulation,  Up: Stack Manipulation

Data stack
----------

`drop'       w -       core       ``drop''

`nip'       w1 w2 - w2       core-ext       ``nip''

`dup'       w - w w       core       ``dup''

`over'       w1 w2 - w1 w2 w1       core       ``over''

`tuck'       w1 w2 - w2 w1 w2       core-ext       ``tuck''

`swap'       w1 w2 - w2 w1       core       ``swap''

`rot'       w1 w2 w3 - w2 w3 w1       core       ``rote''

`-rot'       w1 w2 w3 - w3 w1 w2       gforth       ``not-rote''

`?dup'       w - w       core       ``question-dupe''

`pick'       u - w       core-ext       ``pick''

`roll'       x0 x1 .. xn n - x1 .. xn x0         core-ext       ``roll''

`2drop'       w1 w2 -       core       ``two-drop''

`2nip'       w1 w2 w3 w4 - w3 w4       gforth       ``two-nip''

`2dup'       w1 w2 - w1 w2 w1 w2       core       ``two-dupe''

`2over'       w1 w2 w3 w4 - w1 w2 w3 w4 w1 w2       core       ``two-over''

`2tuck'       w1 w2 w3 w4 - w3 w4 w1 w2 w3 w4       gforth       ``two-tuck''

`2swap'       w1 w2 w3 w4 - w3 w4 w1 w2       core       ``two-swap''

`2rot'       w1 w2 w3 w4 w5 w6 - w3 w4 w5 w6 w1 w2       double-ext       ``two-rote''


File: gforth.info,  Node: Floating point stack,  Next: Return stack,  Prev: Data stack,  Up: Stack Manipulation

Floating point stack
--------------------

`fdrop'       r -       float       ``fdrop''

`fnip'       r1 r2 - r2       gforth       ``fnip''

`fdup'       r - r r       float       ``fdup''

`fover'       r1 r2 - r1 r2 r1       float       ``fover''

`ftuck'       r1 r2 - r2 r1 r2       gforth       ``ftuck''

`fswap'       r1 r2 - r2 r1       float       ``fswap''

`frot'       r1 r2 r3 - r2 r3 r1       float       ``frot''


File: gforth.info,  Node: Return stack,  Next: Locals stack,  Prev: Floating point stack,  Up: Stack Manipulation

Return stack
------------

`>r'       w -       core       ``to-r''

`r>'       - w       core       ``r-from''

`r@'       - w ; R: w - w         core       ``r-fetch''
   copy w from the return stack to the data stack

`rdrop'       -       gforth       ``rdrop''

`2>r'       w1 w2 -       core-ext       ``two-to-r''

`2r>'       - w1 w2       core-ext       ``two-r-from''

`2r@'       - w1 w2       core-ext       ``two-r-fetch''

`2rdrop'       -       gforth       ``two-r-drop''


File: gforth.info,  Node: Locals stack,  Next: Stack pointer manipulation,  Prev: Return stack,  Up: Stack Manipulation

Locals stack
------------


File: gforth.info,  Node: Stack pointer manipulation,  Prev: Locals stack,  Up: Stack Manipulation

Stack pointer manipulation
--------------------------

`sp@'       - a-addr       gforth       ``spat''

`sp!'       a-addr -       gforth       ``spstore''

`fp@'       - f-addr       gforth       ``fp-fetch''

`fp!'       f-addr -       gforth       ``fp-store''

`rp@'       - a-addr       gforth       ``rpat''

`rp!'       a-addr -       gforth       ``rpstore''

`lp@'       - addr         gforth       ``l-p-fetch''

`lp!'       c-addr -       gforth       ``lp-store''


File: gforth.info,  Node: Memory,  Next: Control Structures,  Prev: Stack Manipulation,  Up: Words

Memory
======

* Menu:

* Memory Access::
* Address arithmetic::
* Memory Blocks::

