6502 assembly optimisations: Revision history

18 March 2024

• curprev 21:0621:06, 18 March 2024‎ Fiskbit talk contribs‎ 15,199 bytes 0‎ →‎Avoiding the need for CLC/SEC with ADC/SBC: If carry is clear, SBC should use value-1, not value+1. Thanks to Ooxie for reporting.

20 November 2023

• curprev 13:5613:56, 20 November 2023‎ Qalle talk contribs‎ 15,199 bytes +994‎ test for equality

13 November 2023

• curprev 08:0508:05, 13 November 2023‎ Qalle talk contribs‎ 14,205 bytes −212‎ delete two hints that are more thoroughly explained in the Synthetic instructions article

30 August 2023

• curprev 22:4722:47, 30 August 2023‎ Qalle talk contribs‎ 14,417 bytes +1,147‎ →‎Optimise both speed and size of the code: avoid compare
• curprev 21:0221:02, 30 August 2023‎ Qalle talk contribs‎ 13,270 bytes +6‎ →‎Test whether all specified bits are set, preserving carry: only look up bit pattern once
• curprev 15:3015:30, 30 August 2023‎ Qalle talk contribs‎ 13,264 bytes −16‎ →‎Test whether all specified bits are set, preserving carry: swap EOR/AND for clarity
• curprev 15:2315:23, 30 August 2023‎ Qalle talk contribs‎ 13,280 bytes +53‎ →‎Test whether all specified bits are set, preserving carry: source
• curprev 15:1915:19, 30 August 2023‎ Qalle talk contribs‎ 13,227 bytes +540‎ →‎Optimise both speed and size of the code: test if all bits are set

7 February 2023

• curprev 03:2603:26, 7 February 2023‎ Fiskbit talk contribs‎ 12,687 bytes +193‎ →‎BIT trick: Notes that you can also do this with the zero page version. Notes the caveat that this can trigger register read side-effects.
• curprev 01:4701:47, 7 February 2023‎ Qalle talk contribs‎ 12,494 bytes +957‎ →‎Optimise code size at the expense of cycles: BIT trick

30 January 2023

• curprev 18:0418:04, 30 January 2023‎ Qalle talk contribs‎ 11,537 bytes +151‎ →‎Using relative branch instruction instead of absolute: example

21 October 2020

• curprev 11:2511:25, 21 October 2020‎ Karmic talk contribs‎ 11,386 bytes −52‎ →‎Test bits in decreasing order

16 August 2017

• curprev 08:1908:19, 16 August 2017‎ Qalle talk contribs‎ 11,438 bytes +38‎ identity table: link to main article

26 April 2017

• curprev 07:0907:09, 26 April 2017‎ Bregalad talk contribs‎ 11,400 bytes +28‎ Some rewording - no more 2nd person

22 September 2016

• curprev 20:3020:30, 22 September 2016‎ Tepples talk contribs‎ 11,372 bytes +16‎ →‎Avoiding the need for CLC/SEC with ADC/SBC: Adding a negative may be clearer for subtracting with carry clear

21 September 2016

• curprev 15:5815:58, 21 September 2016‎ Tepples talk contribs‎ 11,356 bytes +659‎ →‎Use Jump tables with RTS instruction instead of JMP indirect instruction: There's one case where this costs memory (Temp in zero page, no tail call, performed at peak stack use) but it's a pure saving in other cases

11 September 2014

• curprev 04:0704:07, 11 September 2014‎ Koitsu talk contribs‎ 10,697 bytes −446‎ Removal of syntax highlighter

25 August 2013

• curprev 07:3007:30, 25 August 2013‎ Koitsu talk contribs‎ 11,143 bytes −100‎ No edit summary

24 August 2013

• curprev 09:1509:15, 24 August 2013‎ Koitsu talk contribs‎ 11,243 bytes +696‎ No edit summary

16 June 2013

• curprev 04:4404:44, 16 June 2013‎ Zzo38 talk contribs‎ 10,547 bytes +836‎ No edit summary

15 June 2013

• curprev 23:0523:05, 15 June 2013‎ Tepples talk contribs‎ 9,711 bytes +345‎ →‎Use a macro instead of a subroutine which is only called once: There's a name for this: Inline expansion. Also loop drawback
• curprev 22:5422:54, 15 June 2013‎ Tepples talk contribs‎ 9,366 bytes +68‎ →‎Avoiding the need for CLC/SEC with ADC/SBC: Example from Apple II
• curprev 22:5222:52, 15 June 2013‎ Tepples talk contribs‎ 9,298 bytes +474‎ →‎Use Jump tables with RTS instruction instead of JMP indirect instruction: Combination with tail call. I've used this, though I forget whether it was in Concentration Room or something else.

8 June 2013

• curprev 03:2903:29, 8 June 2013‎ Tepples talk contribs‎ 8,824 bytes +490‎ Pedants will be pedants. The syntax I added is broken until someone installs Cite.php into this installation of MediaWiki. I may tomorrow.

13 April 2013

• curprev 22:2722:27, 13 April 2013‎ Bisqwit talk contribs‎ m 8,334 bytes +97‎ →‎Avoiding the need for CLC/SEC with ADC/SBC: +example case
• curprev 22:2622:26, 13 April 2013‎ Bisqwit talk contribs‎ 8,237 bytes +467‎ On avoiding CLC&SEC
• curprev 22:0822:08, 13 April 2013‎ Bisqwit talk contribs‎ m 7,770 bytes +2‎ fix header gaffe
• curprev 22:0722:07, 13 April 2013‎ Bisqwit talk contribs‎ 7,768 bytes +718‎ + Use opposite rotate instead of a great number of shifts
• curprev 21:5521:55, 13 April 2013‎ Bisqwit talk contribs‎ 7,050 bytes +13‎ →‎Use an "intelligent" argument system: Mention FDS
• curprev 21:5421:54, 13 April 2013‎ Bisqwit talk contribs‎ 7,037 bytes +178‎ →‎Test bits in decreasing order: On preserving or not preserving A.
• curprev 21:5321:53, 13 April 2013‎ Bisqwit talk contribs‎ 6,859 bytes +269‎ →‎Test bits in decreasing order: On preserving or not preserving A.
• curprev 21:4521:45, 13 April 2013‎ Bisqwit talk contribs‎ 6,590 bytes +31‎ →‎Easily test 2 upper bits of a variable: N&V on "bit" do not depend on A.
• curprev 21:4321:43, 13 April 2013‎ Bisqwit talk contribs‎ 6,559 bytes +152‎ →‎Use Jump tables with RTS instruction instead of JMP indirect instruction: Note about the RTS +1 offset
• curprev 21:3821:38, 13 April 2013‎ Bisqwit talk contribs‎ 6,407 bytes +112‎ →‎Easily test 2 upper bits of a variable: Add "bit" option

12 March 2013

• curprev 22:5622:56, 12 March 2013‎ Lidnariq talk contribs‎ 6,295 bytes +2‎ →‎Logical shift right: misnamed, incorrect '

22 May 2012

• curprev 09:1009:10, 22 May 2012‎ Bregalad talk contribs‎ 6,293 bytes +723‎ No edit summary

30 April 2012

• curprev 01:5501:55, 30 April 2012‎ Tepples talk contribs‎ 5,570 bytes +226‎ CMP #$80 ROR A is also seen in Synthetic instructions
• curprev 01:4901:49, 30 April 2012‎ Tepples talk contribs‎ 5,344 bytes +82‎ →‎Avoid a jsr + rts chain: There's a name for this

28 April 2012

• curprev 13:3513:35, 28 April 2012‎ Tepples talk contribs‎ 5,262 bytes +184‎ →‎Use look-up table to shift right 4 times: Provided that the high nibble is already cleared
• curprev 13:2713:27, 28 April 2012‎ Bregalad talk contribs‎ 5,078 bytes +5,078‎ New page, should be continued