🚀 go-pugleaf

In article <3755@ihlpf.ATT.COM> nevin1@ihlpf.UUCP (00704a-Liber,N.J.) writes:
[admiring the authors of the TRS-80 12K ROM]
>They had to fit all of BASIC in a 12K ROM, and every trick in the book had to
>be used to conserve memory (if I remember correctly, on the original release
>they did it with 8 bytes to spare).  They had to be excellent assembly language
>programmers to find tricks like this!  I take my hat off to these coders (as
>well as the original Apple ROM writers); they did some of the most impressive
>assembly work that I have ever seen!

No, not every trick.

The Z80 has duplicate sets of registers, the alternates being accessed
by one-machine-cycle instructions.  Yet not once did the 12K ROM use
the alternate set.

You would also see sequences similar to

     PUSH  HL                   ;save HL
     LD    HL,(ADDRESS)         ;load HL from memory
     LD    DE,HL                ;transfer to DE
     POP   HL                   ;restore HL

when a simple

     LD    DE,(ADDRESS)         ;load DE from memory

would have sufficed.  And so far as I could tell from disassembled
listings, the BASIC interpreter part of the ROM (as opposed to the 2K
that did the I/O) seldom or never used the index registers, which
I consider to be a very powerful feature of the processor.

Much of the power of the Z80 was wasted in the TRS-80 ROM.
-- 
Rahul Dhesi         UUCP:  <backbones>!{iuvax,pur-ee,uunet}!bsu-cs!dhesi