Overlapping bytemove/longmove/wordmove

rokicki

If the regions pointed to by bytemove are overlapping, in either the
positive or negative direction, is bytemove still guaranteed to do the
right thing? Ditto for the other two. Thanks!

cgracey

You bet! It figures out whether to do a forward or reverse move automatically.

rokicki said...
If the regions pointed to by bytemove are overlapping, in either the
positive or negative direction, is bytemove still guaranteed to do the
right thing? Ditto for the other two. Thanks!

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Chip Gracey
Parallax, Inc.

rokicki

Great!

I'm still confused by a few things though.

If I have:

var long curline, put

what is the difference between the expressions

byte[noparse][[/noparse]curline][noparse][[/noparse]put]

and just

curline[noparse][[/noparse]put] ?

Also, the description of @@ makes me a bit concerned; it says if I have

dat
foo "baz", 0
foo2 "baz2", 0
bar long @foo, @foo2

that I need to use @@bar[noparse][[/noparse]0] and @@bar instead of @bar[noparse][[/noparse]0] and @bar
because the values in bar are not offset by the beginning of the data space.

Can we get a clarification of exactly when we can expect the values to be
so offset, and when we cannot? If I use

x := @foo

in a program, x gets the address of foo, so I don't need to use @@, right?
So why doesn't it when I use

dat
bar long @foo

Thanks for all the help!

cgracey

rokicki said...
Great!

I'm still confused by a few things though.

If I have:

var long curline, put

what is the difference between the expressions

byte[noparse][[/noparse]curline][noparse][[/noparse]put]
Byte[noparse][[/noparse]curline][noparse][[/noparse]put] will access a byte pointed to by 'curline' with 'put' used as a byte·index. In other words, the byte will be located at the value of curline plus the value of put.

and just

curline[noparse][[/noparse]put] ?
Curline[noparse][[/noparse]put] will access the put'th long beginning at the address of curline. Curline is a long, so the index (put) will be shifted left by 2 bits.

Also, the description of @@ makes me a bit concerned; it says if I have

dat
foo "baz", 0
foo2 "baz2", 0
bar long @foo, @foo2

that I need to use @@bar[noparse][[/noparse]0] and @@bar instead of @bar[noparse][[/noparse]0] and @bar
because the values in bar are not offset by the beginning of the data space.

Can we get a clarification of exactly when we can expect the values to be
so offset, and when we cannot? If I use

x := @foo

in a program, x gets the address of foo, so I don't need to use @@, right?
So why doesn't it when I use

dat
bar long @foo

Okay. @@ is used to add the object's base address to some value, usually the address of something in a DAT section. Say you have a list of strings:

DAT
s1·· byte· "This is string 1.",0s2·· byte· "This is string 2. Bla Bla.",0s3·· byte· "This is string 3. Note these all have different lengths.",0s4·· byte· "This is string 4....",0

stringtable word @s1,@s2,@s3,@s4· 'Here is a table of the string offsets within the object

...in a PUB/PRI you could access these strings as an array...

· repeat i from 0 to 3
··· printstring(@@stringtable[noparse][[/noparse]i])

...printstring is some routine which wants the start address of some string in memory. Stringtable is a list of words which contains offsets of various strings. Stringtable[noparse][[/noparse]i] returns the offset of a particular string. The @@ operator adds the object's base address to give you the actual main memory address of string 'i'.

Thanks for all the help!

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Chip Gracey
Parallax, Inc.