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| 1 : | anton | 1.5 | This file describes the implementation model of Gforth. The things |
| 2 : | described herein are valid in all implementations of Gforth. | ||
| 3 : | !! needs updating | ||
| 4 : | anton | 1.1 | |
| 5 : | anton | 1.7 | \ Copyright (C) 1995,2000 Free Software Foundation, Inc. |
| 6 : | anton | 1.5 | |
| 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 | ||
| 21 : | anton | 1.6 | \ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA. |
| 22 : | anton | 1.1 | |
| 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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