Apple-2-SW/apple2_hgr_font_tutorial
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Fix hex literal immediate vals

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Michaelangel007 2016-01-27 15:45:59 -08:00
parent 99f0cf9f99
commit 6c1a2695e2
1 changed files with 10 additions and 10 deletions
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README.md
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@ -1,6 +1,6 @@
#Apple ]\[ //e HGR Font 6502 Assembly Language Tutorial
Revision: 55, Jan 27, 2016.
Revision: 56, Jan 27, 2016.
# Table of Contents
@ -1386,16 +1386,16 @@ That might look like something like this:
ROL ; C=R A=0stuvwPQ
ROL ; C=0 A=stuvwPQR
PHA
AND #1F ; = %000stuvw
AND #$1F ; = %000stuvw
STA _LoadFont+1 ; AddressLo = FontLo + (c*8)
PLA
AND #E0
AND #$E0
CLC
ADC AddressHi
STA _LoadFont+2
```
Hmm, that seems like an **awful lot of work** just for some `bit-shuffling`!! For one thing we're doing a shift and `stuvw` is not taking advantage of it. Can we not we make use of the fact that we will eventually be doing `AND #1F` -> `AND #F8` and `AND #E0` -> `AND #07` ?
Hmm, that seems like an **awful lot of work** just for some `bit-shuffling`!! For one thing we're doing a shift and `stuvw` is not taking advantage of it. Can we not we make use of the fact that we will eventually be doing `AND #1F` -> `AND #$F8` and `AND #E0` -> `AND #07` ?
The **lateral** thinking is to _use partial results_.
@ -1405,11 +1405,11 @@ The **lateral** thinking is to _use partial results_.
2 Q Rstuvw?P
3 R stuvw?PQ
--push A--
stuvw000 <- A & #F8
stuvw000 <- A & #$F8
--store low byte offset--
--pop A--
4 s tuvw?PQR
00000PQR <- A & #07
00000PQR <- A & #$07
--CLC--
--add FontHi to A
--store high byte offset--
@ -1429,7 +1429,7 @@ Listing 7:
033B:2A ROL ; C=Q A=%Rstuvw?P
033C:2A ROL ; C=R A=%stuvw?PQ
033D:AA TAX ; X=%stuvw?PQ push glyph
033E:29 F8 AND #F8 ; A=%stuvw000
033E:29 F8 AND #$F8 ; A=%stuvw000
0340:8D 53 03 STA _LoadFont+1 ; AddressLo = (c*8)
0343:8A TXA ; A=%stuvw?PQ pop glyph
0344:29 03 AND #3 ; Optimization: s=0 implicit CLC !
@ -1448,7 +1448,7 @@ Here is a comparison between the original and final version (clock cycle timings
2 AND #1F 2 ROL
2 ASL 2 ROL
2 ASL 2 TAX
2 ASL 2 AND #F8
2 ASL 2 AND #$F8
2 ADC #<Font 4 STA _LoadFont+1
4 STA _LoadFont+1 2 TXA
4 PLA 2 AND #3
@ -1618,7 +1618,7 @@ Listing 8:
; FUNC: DrawHexNib() = $030C
; PARAM: A = nibble to print as hex char
030A: DrawHexNib
030A:29 0F AND #F ; base 16
030A:29 0F AND #$F ; base 16
030C:AA TAX ;
030D:BD 90 03 LDA NIB2HEX,X ; nibble to ASCII
; intentional fall into PrintChar
@ -2264,7 +2264,7 @@ Here are all the (core) font rendering routines we've entered in so far:
0338:03 68 2A 2A 2A AA 29 F8
0340:8D 53 03 8A 29 03 2A 69
0348:60 8D 54 03 A6 F6 86 FD
0350:A2 00 BD 00 00 91 F5 18
0350:A2 00 BD 00 60 91 F5 18
0358:A5 F6 69 04 85 F6 E8 E0
0360:08 D0 EF C8 A6 FD 86 F6
0368:60