Annotation of gforth/asm/bitmask.fs, revision 1.7

1.1       pazsan      1: \ bitmask.fs Generic Bitmask compiler                                  13aug97jaw
                      2: 
1.7     ! anton       3: \ Copyright (C) 1998,2000,2003,2007 Free Software Foundation, Inc.
1.2       anton       4: 
                      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
1.6       anton       9: \ as published by the Free Software Foundation, either version 3
1.2       anton      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
1.6       anton      18: \ along with this program. If not, see http://www.gnu.org/licenses/.
1.1       pazsan     19: 
                     20: \ This is a tool for building up assemblers.
                     21: \ In modern CPU's instrutions there are often some bitfields that
                     22: \ sepcify a register, a addressing mode, an immediate value.
                     23: \ A value in an instruction word might be represented in one bitfield
                     24: \ or several bitfields.
                     25: \ If you code it yourself, you have to think about the right shifting
                     26: \ operators. E.g. if you want to store a 2-bit value at bit position 3
                     27: \ you would code: ( value opcode -- opcode ) swap 3 lshift or
                     28: \ If the value is stored at bit-position 2-3 and 5-6 it gets more difficult:
                     29: \ ( value opcode -- opcode ) swap dup 3 and 2 lshift rot or swap 3 and 5 lshift or
                     30: \ This is no fun! This can be created automatically by: "maskinto %bitfield".
                     31: \ This compiles some code like above into the current definition.
                     32: \ This code has the same stack-effect then our examples.
                     33: \ Additional things compiled: A check whether the value could be represented
                     34: \ by the bitfield, the area of the bitfield is cleared in the opcode.
                     35: 
                     36: \ Code Compliance:
                     37: \
                     38: \ This is for 32 bit and 64 bit systems and for GForth only.
                     39: \ 
                     40: 
                     41: \ Revision Log:
                     42: \
                     43: \ 13aug97 Jens Wilke   Creation
                     44: 
                     45: decimal
                     46: 
                     47: : ?bitexceed ( u1 u2 -- u1 )
                     48: \G if u1 is greater than u2 the value could not be represented in the bitfield
                     49:   over u< ABORT" value exceeds bitfield!" ;
                     50: 
                     51: : bitset# ( u -- )
                     52: \G returns the number of bits set in a cell
                     53:   0 swap 64 0 DO dup 1 and IF swap 1+ swap THEN 1 rshift LOOP drop ;
                     54: 
                     55: : max/bits ( u -- u2 )
                     56: \G returns the highes number that could be represented by u bits
                     57:   1 swap lshift 1- ;
                     58: 
                     59: Variable mli   \ masked last i
                     60: Variable mst   \ masked state
                     61: 
                     62: : (maskinto) ( n -- )
                     63:   0 mst !
                     64:   0 mli !
                     65:   [ -1 bitset# ] literal 0
                     66:   DO   mst @
                     67:        IF      dup 1 and 0=
                     68:                IF I mli @ - ?dup 
                     69:                   IF   postpone dup max/bits mli @ lshift
                     70:                        postpone literal postpone and postpone rot 
                     71:                        postpone or postpone swap
                     72:                   THEN
                     73:                   I mli ! 0 mst !
                     74:                THEN
                     75:        ELSE    dup 1 and
                     76:                IF I mli @ - ?dup
                     77:                   IF postpone literal postpone lshift THEN
                     78:                   I mli ! 1 mst !
                     79:                THEN
                     80:        THEN
                     81:        1 rshift 
                     82:   LOOP drop 
                     83:   postpone drop ;
                     84: 
                     85: : maskinto ( <mask> )
                     86:   name s>number drop
                     87:   \ compile: clear maskarea
                     88:   dup invert 
                     89:   postpone literal postpone and postpone swap
                     90:   \ compile: make check
                     91:   dup bitset# max/bits
                     92:   postpone literal postpone ?bitexceed
                     93:   (maskinto) ; immediate
                     94: 
                     95: \ : test maskinto %110010 ;

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