\ bitmask.fs Generic Bitmask compiler 13aug97jaw
\ This file is copyritghted by JW-Datentechnik GmbH, Munich.
\ You have the right to use it together with GForth EC.
\ This file may copied and redistributed if it is not altered.
\ This is distributed without any warranty.
\ Send comments, suggestions, additions and bugfixes to: email@example.com
\ This is a tool for building up assemblers.
\ In modern CPU's instrutions there are often some bitfields that
\ sepcify a register, a 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
: ?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 highes 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
I mli ! 0 mst !
ELSE dup 1 and
IF I mli @ - ?dup
IF postpone literal postpone lshift THEN
I mli ! 1 mst !
postpone drop ;
: maskinto ( <mask> )
name s>number drop
\ compile: clear maskarea
postpone literal postpone and postpone swap
\ compile: make check
dup bitset# max/bits
postpone literal postpone ?bitexceed
(maskinto) ; immediate
\ : test maskinto %110010 ;