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\ bitmask.fs Generic Bitmask compiler 13aug97jaw
\ Copyright (C) 1998,2000,2003,2007 Free Software Foundation, Inc.
\ This file is part of Gforth.
\ Gforth is free software; you can redistribute it and/or
\ modify it under the terms of the GNU General Public License
\ as published by the Free Software Foundation, either version 3
\ of the License, or (at your option) any later version.
\ This program is distributed in the hope that it will be useful,
\ but WITHOUT ANY WARRANTY; without even the implied warranty of
\ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
\ GNU General Public License for more details.
\ You should have received a copy of the GNU General Public License
\ along with this program. If not, see http://www.gnu.org/licenses/.
\ This is a tool for building up assemblers.
\ In modern CPU's instructions there are often some bitfields that
\ specify a register, an addressing mode, an immediate value.
\ A value in an instruction word might be represented in one bitfield
\ or several bitfields.
\ If you code it yourself, you have to think about the right shifting
\ operators. E.g. if you want to store a 2-bit value at bit position 3
\ you would code: ( value opcode -- opcode ) swap 3 lshift or
\ If the value is stored at bit-position 2-3 and 5-6 it gets more difficult:
\ ( value opcode -- opcode ) swap dup 3 and 2 lshift rot or swap 3 and 5 lshift or
\ This is no fun! This can be created automatically by: "maskinto %bitfield".
\ This compiles some code like above into the current definition.
\ This code has the same stack-effect then our examples.
\ Additional things compiled: A check whether the value could be represented
\ by the bitfield, the area of the bitfield is cleared in the opcode.
\ Code Compliance:
\
\ This is for 32-bit and 64-bit systems and for GForth only.
\
\ Revision Log:
\
\ 13aug97 Jens Wilke Creation
decimal
: ?bitexceed ( u1 u2 -- u1 )
\G if u1 is greater than u2 the value could not be represented in the bitfield
over u< ABORT" value exceeds bitfield!" ;
: bitset# ( u -- )
\G returns the number of bits set in a cell
0 swap 64 0 DO dup 1 and IF swap 1+ swap THEN 1 rshift LOOP drop ;
: max/bits ( u -- u2 )
\G returns the highest number that could be represented by u bits
1 swap lshift 1- ;
Variable mli \ masked last i
Variable mst \ masked state
: (maskinto) ( n -- )
0 mst !
0 mli !
[ -1 bitset# ] literal 0
DO mst @
IF dup 1 and 0=
IF I mli @ - ?dup
IF postpone dup max/bits mli @ lshift
postpone literal postpone and postpone rot
postpone or postpone swap
THEN
I mli ! 0 mst !
THEN
ELSE dup 1 and
IF I mli @ - ?dup
IF postpone literal postpone lshift THEN
I mli ! 1 mst !
THEN
THEN
1 rshift
LOOP drop
postpone drop ;
: maskinto ( <mask> )
name s>number drop
\ compile: clear maskarea
dup invert
postpone literal postpone and postpone swap
\ compile: make check
dup bitset# max/bits
postpone literal postpone ?bitexceed
(maskinto) ; immediate
\ : test maskinto %110010 ;
|
