File:  [gforth] / gforth / README.vmgen
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    1: Vmgen supports the construction of interpretive systems by generating
    2: the code for executing and dealing with virtual machine (VM)
    3: instructions from simple descriptions of the VM instructions.
    4: 
    5: This file is about Vmgen-specific issues.  Issues affecting both
    6: Gforth and Vmgen (e.g., platform compatibility) are discussed in
    7: README.
    8: 
    9: Vmgen generates code for executing VM instructions (with optional
   10: tracing), for generating VM code, for disassembling VM code, and for
   11: profiling VM instruction sequences.  A VM instruction description
   12: looks like this:
   13: 
   14: add  ( i1 i2 -- i )
   15: i = i1+i2;
   16: 
   17: Vmgen supports several techniques for writing efficient interpreters:
   18: virtual machine interpreters, threaded code, combining VM instructions
   19: into superinstructions, keeping the top-of-stack in a register,
   20: scheduling the dispatch of the next VM instruction, and a couple of
   21: minor optimizations.  Interpreters created with Vmgen usually are
   22: faster than competing interpreters and are typically only a factor of
   23: 2-10 slower than the code generateed by native-code compilers.
   24: 
   25: Vmgen has special support for stack-based VMs (but it can also be
   26: used to advantage when implementing a register-based VM).
   27: 
   28: Changes in Vmgen from earlier releases are explained in NEWS.vmgen.
   29: 
   30: After installation the documentation is available in info form and in
   31: printable form (doc/vmgen.ps).
   32: 
   33: There is a simple usage example in vmgen-ex (and a variation on that
   34: in vmgen-ex2).  See the documentation for more information on that.
   35: 
   36: To report a bug, use
   37: <https://savannah.gnu.org/bugs/?func=addbug&group_id=2672>.  For
   38: discussion on Vmgen (e.g., how to use it), use the
   39: bug-vmgen@mail.freesoftware.fsf.org mailing list (use
   40: <http://mail.gnu.org/mailman/listinfo/help-vmgen> to subscribe).
   41: 
   42: You can find vmgen at http://www.complang.tuwien.ac.at/anton/vmgen/.
   43: 
   44: Vmgen is currently distributed with Gforth (because it needs Gforth to
   45: run, and Gforth needs it to build), and is installed together with
   46: Gforth (read INSTALL for instructions).
   47: 
   48: Note that future versions of vmgen may require small changes in
   49: programs written for the present version (e.g., requiring a few
   50: additional macro definitions).
   51: 
   52: -----
   53: Copyright (C) 2001, 2002, 2003,2007 Free Software Foundation, Inc.
   54: 
   55: This file is part of Gforth.
   56: 
   57: Gforth is free software; you can redistribute it and/or
   58: modify it under the terms of the GNU General Public License
   59: as published by the Free Software Foundation, either version 3
   60: of the License, or (at your option) any later version.
   61: 
   62: This program is distributed in the hope that it will be useful,
   63: but WITHOUT ANY WARRANTY; without even the implied warranty of
   64: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.#See the
   65: GNU General Public License for more details.
   66: 
   67: You should have received a copy of the GNU General Public License
   68: along with this program. If not, see http://www.gnu.org/licenses/.

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