Hiya Spiro, The routines are not out of context because they are not part of a larger program. I typed them in exactly as they are presented in the book, except the comments are mine. The only command I left out of each code snippet was the BRK at the end of each. Besides, its ABSURD to assume that SED is the default condition for the entire program. NO-ONE programs this way. Even Leventhal recommends keeping D clear outside of subroutines! For that reason I say its QUITE FAIR to include SED and CLD in the cycle count. Here're two sample routines I cooked up to test your second statement: ; CONVERT 1 BYTE AND STORE IN $FB, $FC TAX ; 2 CYCLES LSR ; 2 CYCLES LSR ; 2 CYCLES LSR ; 2 CYCLES LSR ; 2 CYCLES JSR MAKEDIG ; 6 CYCLES STA $FB ; 3 CYCLES TXA ; 2 CYCLES AND #$0F ; 2 CYCLES ; 2 ITERATIONS OF FOLLOWING CODE MAKEDIG CMP #$0A ; 2x2=4 CYCLES BCC DIGIT ; 4x2=8 CYCLES (WORST CASE) ADC #$06 ; 2x2=4 CYCLES DIGIT ADC #$30 ; 2x2=4 CYCLES STA $FC ; 3x2=6 CYCLES RTS ; 6x2=12 CYCLES ; 61 CYCLES TOTAL ; TRY DECIMAL MODE ALGORITHM TAX ; 2 CYCLES LSR ; 2 CYCLES LSR ; 2 CYCLES LSR ; 2 CYCLES LSR ; 2 CYCLES SED ; 2 CYCLES JSR MAKEDIG ; 6 CYCLES STA $FB ; 3 CYCLES TXA ; 2 CYCLES AND #$0F ; 2 CYCLES ; 2 ITERATIONS FOLLOWING CODE MAKEDIG CLC ; 2x2=4 CYCLES ADC #$90 ; 2x2=4 CYCLES ADC #$40 ; 2x2=4 CYCLES CLD ; 2x2=4 CYCLES STA $FC ; 3x2=6 CYCLES RTS ; 6x2=12 CYCLES ; 59 CYCLES TOTAL Looks like you were correct Spiro! Now, I suppose I can further optimise it by removing the subroutine calls and using straight-line code: SED TAX LSR LSR LSR LSR CLC ADC #$90 ADC #$40 STA $FB TXA AND #$0F ; *Can this be omitted? CLC ; **IS THIS EVEN NECESSARY? ADC #$90 ADC #$40 STA $FC CLD ; 36 cycles. BLAZING FAST! * I dont' think its really necessary to mask out the high nybble here. Since there is no CoMParison to do, the extra nybble should just overflow thru the Carry and out into the binary ether, right??? ** I'm pretty damn sure that the first instance of ADC #$40 will eat any carry. Thus, C is already clear for the low nybble. CHALLENGE! - Can ANYONE further optomise this code for SPEED? Is there a different algorithm even FASTER than this? ASIDE - I'm inexperienced with 6502 decimal mode operations. I was SHOCKED to discover that in decimal mode $0A is treated as 10 'ones' units! :-O Thus LDA #$0A SED CLC ADC #$00 will leave $10 in the Accumulator! NEATO! :-)) Thanx for making me THINK Spiro! :-) --- Spiro Trikaliotis <Trikemail@example.com> wrote: > Hi, > > > In the book '6502 Assembly Language Programming' > by > > Lance Leventhal, it is stated that > > SED ; 2 cycles > > CLC ; 2 cycles > > LDA $40 ; 3 cycles > > ADC #$90 ; 2 cycles > > ADC #$40 ; 2 cycles > > STA $41 ; 3 cycles > > CLD ; 2 cycles > > ; 16 cycles total > > > > is 'quicker' than > > > > LDA $40 ; 3 cycles > > CMP #10 ; 2 cycles > > BCC ASCZ ; 2/3/4 cycles > > ; 2=no branch / 3=branch / 4=cross-page branch > > ADC #'A'-'9'-'2' ; 2 cycles > > ASCZ ADC #'0' ; 2 cycles > > STA $41 ; 3 cycles > > ; 13/14 cycles total > > > Have I miscounted my cycles? Is there ANY > circumstance > > under which the first routine is 'quicker' than > the > > second??? :-/ > > I don't think you have miscounted your cycles. But, > IMHO, is not fair to > count SED and CLD in the first case! Why? There are > two reasons: > > 1. These routines are here w/o context; we do not > know if outside of the > hex-to-ascii-conversion, the decimal flag has to be > set or not. If it has to > be set all the times, then you can add these two > instructions to the 2nd > case, resulting in 12 cycles for the first / 17/18 > cycles for the second > case. > > 2. When converting like here, it is unlikely that > you will have to convert > just one digit. So, when you have to convert, for > example, 4 digits, then > you have to SED and CLD only once (if you arrange > your conversion in a good > maner). > > Spiro. > > - > This message was sent through the cbm-hackers > mailing list. > To unsubscribe: echo unsubscribe | mail firstname.lastname@example.org. ===== Get a FREE 6Mb webmail box from go6502! - http://www.geocities.com/profdredd As low as 2.99% Intro APR from NextCard! - http://www.nextcard.com/index6.html?ref=aff0074521 PayPal is the FAST FREE and SECURE way to send money! - https://secure.paypal.x.com/refer/pal=profdredd%40yahoo.com __________________________________________________ Do You Yahoo!? Yahoo! Auctions - Buy the things you want at great prices. http://auctions.yahoo.com/ - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail email@example.com.
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