X-Git-Url: https://git.gag.com/?a=blobdiff_plain;f=doc%2Fchoices.txt;h=9fa79244d309fd21e6a9d491a227ded83bbf179e;hb=b5d29d69138a09774f423a86270ca058a545cfd2;hp=080b0cf24a948918414914c1b83e3e6974a78d43;hpb=a408f6fc31450c42a558611971841af32c4edff4;p=fw%2Fsdcc

diff --git a/doc/choices.txt b/doc/choices.txt
index 080b0cf2..9fa79244 100644
--- a/doc/choices.txt
+++ b/doc/choices.txt
@@ -35,4 +35,75 @@ On stack word push
 	 inc  hl
 	 ld   d,(hl)
    1 = d + 8 + 8 + 4
-   2 = d + 8 + 8 + 8
\ No newline at end of file
+   2 = d + 8 + 8 + 8
+
+Structure member get:
+   Normally fetch pair
+   Then add pair and constant with result in hl
+
+   ld	l,c	; 4
+   ld	h,b	; 4
+   inc  hl ..	; 6	= 8 + 6n
+or
+   ld	l,c	; 4
+   ld	h,b	; 4
+   ld	a,#0x06	; 7
+   add	a,c	; 4
+   ld	l,a	; 4
+   ld	a,#0x00 ; 7
+   adc	a,b	; 4
+   ld	h,a	; 4	= 38
+alt: (only when result=hl and left, rigth = pair, const)
+   ld	   hl,#const	; 10
+   add	   hl,pair	; 11	= 21
+
+So (1) is best for n <= 2, (2) is just bad, (3) is good n > 2
+
+How about:
+    pair = pair + constant:
+1:
+    ld	a,#0x08	; 7
+    add	a,c	; 4
+    ld	c,a	; 4
+    ld	a,#0x00	; 7
+    adc	a,b	; 4
+    ld	b,a	; 4	= 30
+2:
+	ld	hl,#const	; 10
+	add	hl,pair		; 11
+	ld	c,l		; 4
+	ld	b,h		; 4	= 29
+One cycle.  If I cache HL later it will throw away the advantage.  Choose 1.
+
+PlusIncr on pairs:
+1:
+	 inc	pair		; 6 	= 6n
+2:
+	ld	a,#0x04		; 7
+	add	a,c		; 4
+	ld	c,a		; 4
+	ld	a,#0x00		; 7
+	adc	a,b		; 4
+	ld	b,a		; 4 	= 30
+So n <= 5 (1) is better.
+
+Frame pointer:
+It's nice to use HL as the temp register, but what if I used it as the
+frame pointer instead of ix?
+
+Instead of:
+	ld	e,5(ix)		; 19
+	ld	d,6(ix)		; 19	= 38
+
+	ld	hl,#5		; 10
+	add	hl,sp		; 11
+	ld	e,(hl)		; 7
+	inc	hl		; 6
+	ld	d,(hl)		; 7	= 41
+
+Things get better when you access the same set over, as you get rid
+of the setup.  But they get worse when both ops are on the stack/in
+direct space.  Easiest this way for now.  iy may benifit...
+
+	
+