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--- base:advanced_optimizing [2016-02-04 20:48] – [DCP/ISC] bitbreaker
+++ base:advanced_optimizing [2017-03-04 22:25] – [DCP/ISC] monte_carlos
@@ Line 1154: / Line 1154: @@
 Another good use can be made if you want to do a inc/dec ($xx),y what is actually not available. So here isc/dcp ($xx),y will help you out, as it is also available for the indirect y adressing mode.
+f.e.:
+<code>
+ldy #..
+lda (zp),y
+clc
+adc #..
+sta (zp),y
+bcc +
+iny
+isc (zp),y
++
+</code>
+or
+<code>
+ldy #..
+lda (zp),y
+sec
+sbc #..
+sta (zp),y
+bcs +
+iny
+dcp (zp),y
++
+</code>
 For decrementing a 16 bit pointer it is also of good use:
@@ Line 1345: / Line 1372: @@
 So always try to form the term into something new and see if it performs better this way. So just remember the simple mathematic laws.
+Now also think of that classical negation term:
+<code>
+          lda num
+          eor #$ff
+          clc
+          adc #$01
+          sta neg
+</code>
+Depending on what you have in register A, you can express it in many differnet ways:
+<code>
+          ;a = $ff; carry set
+          eor num
+          adc #$00
+          sta neg
+          ;a = $00; carry set;
+          sbc num
+          sta neg
+          ;a = $ff; carry clear
+          adc num
+          eor #$ff
+          sta neg
+          ;a = $00; carry clear;
+          adc #$01
+          sbc num
+          sta neg
+</code>
+There are of course also other expressions possible, just ponder a while about the term.
 ====== Running out of registers ======