Yeah, i try to avoid IF..THEN wherever I can, especially if it requires an
extra line.
It does give some strange-looking code though, like line 40 in the HEX to
decimal conversion in my dump program that conditionally converts the from/to
address digits to upper case if necessary by subtracting 32 (a simple AND 95
would probably have been simpler ;-) )
Convert up to 4 HEX digits in X$ to decimal equivalent in X:
20 X=0:X$=RIGHT$("0000"+X$,4)
30 FORI=1TO4:Y=ASC(MID$(X$,I,1))
40 Y$=CHR$(Y+(Y>95)*32)
50 L=INSTR(1,H,Y$)-1:X=X+L*(16^(4-I))
----- Original Message -----
From: John R. Hogerhuis
To: [email protected]
Sent: Thursday, October 27, 2022 5:19 PM
Subject: Re: [M100] Compute a 16-bit signed value in BASIC
I was curious if loading a string pointer could be done without an explicit
IF.
Seems like what we're doing is J as LSB, K as MSB
K>127: J + K*256-65536
or
K<=127: J + K*256 - 0
Taking J + K * 256 - 65536
factoring out 256 and putting both functions in a similar form:
K > 127: J + 256 ( K - 256)
K <= 127: J + 256 ( K - 0 )
Knowing comparisons can be done without 'IF'... if an expression is true you
get -1 and 0 if false, we can inline the conditional into the expression
So the computation without IF would be
J + 256% * ( K + 256% * (K > 127%))
So something like this:
10 DEFINTP:DEFSTRH
20 H=CHR$(201)
30 P=VARPTR(H)+1
1000 P=PEEK(P)+256%*(PEEK(P+1)+256%*(PEEK(P+1)>127))
1010 PRINTP
Not sure if this works, particularly with the integer constants. And there
might be speed optimizations... certainly it is doing the MSB peek twice.
-- John.
