QUICK PEEK (1K ZX81)
by Alan Potter, Glasgow
from Your Computer (December 1982), page 109

In many BASIC 1K games there is a line similar to:

    LET A=PEEK (PEEK 16398+256*PEEK 16399)

This line tests to see if the next position in the display file to be
Printed has anything in it, and, if so, what it is.

    (PEEK 16398+256*PEEK 16399)

gives the address of the next position to be Printed, and this line Peeks
into that address to see what is there.

This is a useful line, but time-consuming and heavy on memory. I have
written a machine-code routine which duplicates this function, and is
faster while using less memory, which, as any 1K user knows is a great help.

When this routine is called by a USR 16514 function, on return it will give
the equivalent of the earlier Peek.

For those experienced in machine code, the routine may be stored anywhere
since it contains no jumps.
