MemAnd, MemOr and MemXor Commands

Purpose

Perform a logical bit-wise operation on two bit patterns in memory.

Syntax

MemAnd [(] src_addr,dst_addr,count [)]

MemOr [(] scr_addr, dst_addr, count [)]

MemXor [(] scr_addr, dst_addr, count [)]

Description

Each command performs a different logical bit-wise operation on two bit patterns in memory:

• MemAnd performs an AND, which results in the target bits being set only when the corresponding bits are set in both source and target area.
• MemOr an OR, results in the target bits being set when either the source or the target bits are also set.
• MemXor an XOR, which results in the target bits being set when the bits are set in either the source or target but not both.

In all cases, scr_addr specifies the address of the source, dst_addr the address of the destination location, and count specifies the number of bytes to use at both locations. The logical And results in the target bits being set only when the corresponding bits are set in both source and target area.

Example

OpenW 1

Win_1.FontTransparent = True                      // Needed to print properly on Win8/10

Local a%

Global a?(15), b?(15)

a?(9) = -1, b?(9) = -1, b?(10) = -1, b?(12) = -1  // Set initial flags

test("Before any operations:")

MemAnd V:a?(0), V:b?(0), (Dim?(a?()) + 7) >> 3    // Only b?(9) remains set

test("After MemAnd:")

b?(9) = -1, b?(10) = -1, b?(12) = -1              // Reset flags for MemOr

MemOr V:a?(0), V:b?(0), (Dim?(a?()) + 7) >> 3     // b?(9), b?(10) and b?(12) remain set

@test("After MemOr:")

b?(9) = -1, b?(10) = -1, b?(12) = -1              // Reset flags for MemXor

MemXor V:a?(0), V:b?(0), (Dim?(a?()) + 7) >> 3    // b?(9) is reset

@test("After MemXor:")

Procedure test(txt$)

Local i%

Print txt$

Print "a?() - ";

For i% = 0 To 15 : Print Str$(a?(i%), 2, 0)` : Next : Print

Print "b?() - ";

For i% = 0 To 15 : Print Str$(b?(i%), 2, 0)` : Next : Print

Print

EndProc

Remarks

This method of memory manipulation can be particularly handy for use with databases. For example, if a database contains variables which are used as flags to mark (-1) or not to mark (0) an attribute, these method of memory manipulation can be very helpful. Using MemAnd an inquiry can be made to see if the markers apply to one or both attributes, with MemOr to see if the markers apply to either one or both attributes, while with MemXor an inquiry can be made to see if the markers apply to one or the other but not both attributes..

{Created by Sjouke Hamstra; Last updated: 04/03/2017 by James Gaite}