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*Sat May 8 10:50:44 2010 UTC* (10 years, 3 months ago) by *dvdkhlng*

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Branches: MAIN

CVS tags: HEAD

changed operand order of 'embed' to be closer to maskinto. this should be more usable in practice.

\ Rewritten and improved bitmask code \ Author: David Kühling <dvdkhlng AT gmx DOT de> \ Created: May 2010 \ Copyright (C) 2010 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/. : bitset? ( x #bit -- flag ) \ get value of single bit in cell x rshift 1 and ; : setbit ( x1 0|1 #bit -- x2 ) \ set value of single bit in cell x 1 over lshift invert -rot \ mask for deleting bit lshift \ mask for optionally setting bit -rot and or ; \ first delete then optionally set bit : (bits/cell) ( -- +n ) \ measure number of bits per cell 1 1 begin 1 lshift dup while swap 1+ swap repeat drop ; (bits/cell) CONSTANT bits/cell : dispense ( x1-val x2-mask -- x3-masked ) \ encode val into the bits given by mask. bits in mask can be spread out \ as much as you like. for signed values 'val', first apply 'narrow' below bits/cell 0 do \ iterate over bits in mask dup i bitset? if \ if mask bit set: over 1 and i setbit \ replace bit in mask by val's bit swap 1 rshift swap \ and remove bit from val then loop swap 0<> ABORT" dispense: value does not fit into masked bits" ; : embed ( x2-val x1-accu x3-mask -- x4-result ) \ encode 'val' into bits given by mask, replacing these bits in 'accu' tuck invert and -rot \ delete corresponding bits in accu dispense or ; \ dispense value over masked bits, onto accu ; : mask ( +n -- mask ) \ get bitmask for lowest #n bits 0 invert swap lshift invert ; : narrow ( n1 n2 -- x ) \ limit signed value to n2 bits \ note: assumes 2-complement number n1 and 2-complement host 2dup mask and -rot \ compute masked value, 1- \ but before returning, check whether no bits lost -1 over lshift ( lower bund) 1 rot lshift ( upper bound) within 0= ABORT" narrow: signed value out of range" ; : maskinto ( "x-mask" -- runtime: x1-val x1-accu -- x2-masked ) \ for backwards compatability with old bitmask code parse-word s>number drop ]]L embed [[ ; IMMEDIATE

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