Annotation of gforth/model, revision 1.7

1.5       anton       1: This file describes the implementation model of Gforth. The things
                      2: described herein are valid in all implementations of Gforth.
                      3: !! needs updating
1.1       anton       4: 
1.7     ! anton       5: \ Copyright (C) 1995,2000 Free Software Foundation, Inc.
1.5       anton       6: 
                      7: \ This file is part of Gforth.
                      8: 
                      9: \ Gforth is free software; you can redistribute it and/or
                     10: \ modify it under the terms of the GNU General Public License
                     11: \ as published by the Free Software Foundation; either version 2
                     12: \ of the License, or (at your option) any later version.
                     13: 
                     14: \ This program is distributed in the hope that it will be useful,
                     15: \ but WITHOUT ANY WARRANTY; without even the implied warranty of
                     16: \ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
                     17: \ GNU General Public License for more details.
                     18: 
                     19: \ You should have received a copy of the GNU General Public License
                     20: \ along with this program; if not, write to the Free Software
1.6       anton      21: \ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
1.1       anton      22: 
                     23: The instruction pointer (ip) is post-incremented.
                     24: 
                     25: Branches are relative:
                     26:        branch
                     27: offset:        target - offset
                     28:        ...
                     29: target:        ...
                     30: 
                     31: The top-of return stack is in memory
                     32: 
                     33: The top of data stack need not be in memory. Other data stack items
                     34: are in memory.
                     35: 
                     36: The stacks grow downward
                     37: 
                     38: flags are represtented by 0 and -1
                     39: 
                     40: The loop control parameters are the index on the top of return stack
                     41: and the limit on the second item.
                     42: 
                     43: Everything except the virtual machine registers (ip, sp, etc.) is
                     44: addressable.
                     45: 
                     46: The return address on the return stack occupies one cell.
                     47: 
                     48: There is a floating point stack
                     49: The floating point numbers are the same as C's double numbers
                     50: 
                     51: The error returns of the file word set are FALSE or TRUE. (or should
                     52: we use errno? Does this work with stdio functions?)
                     53: 
                     54: No assumptions can be made about the order of fetching the xt of the
                     55: next word wrt the other operations in a forth word. This makes a
                     56: difference only if you want to execute code lying on the stack or if
                     57: you store into the very next word that is executed.

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