[gforth] / gforth / asm / bitmask.fs  

gforth: gforth/asm/bitmask.fs

1 : pazsan 1.1 \ bitmask.fs Generic Bitmask compiler 13aug97jaw
2 :    
3 : anton 1.4 \ Copyright (C) 1998,2000 Free Software Foundation, Inc.
4 : anton 1.2
5 :     \ This file is part of Gforth.
6 :    
7 :     \ Gforth is free software; you can redistribute it and/or
8 :     \ modify it under the terms of the GNU General Public License
9 :     \ as published by the Free Software Foundation; either version 2
10 :     \ of the License, or (at your option) any later version.
11 :    
12 :     \ This program is distributed in the hope that it will be useful,
13 :     \ but WITHOUT ANY WARRANTY; without even the implied warranty of
14 :     \ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 :     \ GNU General Public License for more details.
16 :    
17 :     \ You should have received a copy of the GNU General Public License
18 :     \ along with this program; if not, write to the Free Software
19 : anton 1.3 \ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
20 : pazsan 1.1
21 :     \ This is a tool for building up assemblers.
22 :     \ In modern CPU's instrutions there are often some bitfields that
23 :     \ sepcify a register, a addressing mode, an immediate value.
24 :     \ A value in an instruction word might be represented in one bitfield
25 :     \ or several bitfields.
26 :     \ If you code it yourself, you have to think about the right shifting
27 :     \ operators. E.g. if you want to store a 2-bit value at bit position 3
28 :     \ you would code: ( value opcode -- opcode ) swap 3 lshift or
29 :     \ If the value is stored at bit-position 2-3 and 5-6 it gets more difficult:
30 :     \ ( value opcode -- opcode ) swap dup 3 and 2 lshift rot or swap 3 and 5 lshift or
31 :     \ This is no fun! This can be created automatically by: "maskinto %bitfield".
32 :     \ This compiles some code like above into the current definition.
33 :     \ This code has the same stack-effect then our examples.
34 :     \ Additional things compiled: A check whether the value could be represented
35 :     \ by the bitfield, the area of the bitfield is cleared in the opcode.
36 :    
37 :     \ Code Compliance:
38 :     \
39 :     \ This is for 32 bit and 64 bit systems and for GForth only.
40 :     \
41 :    
42 :     \ Revision Log:
43 :     \
44 :     \ 13aug97 Jens Wilke Creation
45 :    
46 :     decimal
47 :    
48 :     : ?bitexceed ( u1 u2 -- u1 )
49 :     \G if u1 is greater than u2 the value could not be represented in the bitfield
50 :     over u< ABORT" value exceeds bitfield!" ;
51 :    
52 :     : bitset# ( u -- )
53 :     \G returns the number of bits set in a cell
54 :     0 swap 64 0 DO dup 1 and IF swap 1+ swap THEN 1 rshift LOOP drop ;
55 :    
56 :     : max/bits ( u -- u2 )
57 :     \G returns the highes number that could be represented by u bits
58 :     1 swap lshift 1- ;
59 :    
60 :     Variable mli \ masked last i
61 :     Variable mst \ masked state
62 :    
63 :     : (maskinto) ( n -- )
64 :     0 mst !
65 :     0 mli !
66 :     [ -1 bitset# ] literal 0
67 :     DO mst @
68 :     IF dup 1 and 0=
69 :     IF I mli @ - ?dup
70 :     IF postpone dup max/bits mli @ lshift
71 :     postpone literal postpone and postpone rot
72 :     postpone or postpone swap
73 :     THEN
74 :     I mli ! 0 mst !
75 :     THEN
76 :     ELSE dup 1 and
77 :     IF I mli @ - ?dup
78 :     IF postpone literal postpone lshift THEN
79 :     I mli ! 1 mst !
80 :     THEN
81 :     THEN
82 :     1 rshift
83 :     LOOP drop
84 :     postpone drop ;
85 :    
86 :     : maskinto ( <mask> )
87 :     name s>number drop
88 :     \ compile: clear maskarea
89 :     dup invert
90 :     postpone literal postpone and postpone swap
91 :     \ compile: make check
92 :     dup bitset# max/bits
93 :     postpone literal postpone ?bitexceed
94 :     (maskinto) ; immediate
95 :    
96 :     \ : test maskinto %110010 ;
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