Annotation of gforth/model, revision 1.10

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: 
1.10    ! anton       5: \ Copyright (C) 1995,2000,2003,2007 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
1.9       anton      11: \ as published by the Free Software Foundation, either version 3
1.5       anton      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
1.9       anton      20: \ along with this program. If not, see http://www.gnu.org/licenses/.
1.1       anton      21: 
                     22: The instruction pointer (ip) is post-incremented.
                     23: 
                     24: Branches are relative:
                     25:        branch
                     26: offset:        target - offset
                     27:        ...
                     28: target:        ...
                     29: 
                     30: The top-of return stack is in memory
                     31: 
                     32: The top of data stack need not be in memory. Other data stack items
                     33: are in memory.
                     34: 
                     35: The stacks grow downward
                     36: 
                     37: flags are represtented by 0 and -1
                     38: 
                     39: The loop control parameters are the index on the top of return stack
                     40: and the limit on the second item.
                     41: 
                     42: Everything except the virtual machine registers (ip, sp, etc.) is
                     43: addressable.
                     44: 
                     45: The return address on the return stack occupies one cell.
                     46: 
                     47: There is a floating point stack
                     48: The floating point numbers are the same as C's double numbers
                     49: 
                     50: The error returns of the file word set are FALSE or TRUE. (or should
                     51: we use errno? Does this work with stdio functions?)
                     52: 
                     53: No assumptions can be made about the order of fetching the xt of the
                     54: next word wrt the other operations in a forth word. This makes a
                     55: difference only if you want to execute code lying on the stack or if
                     56: you store into the very next word that is executed.

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