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- ; *** Requirements ***
- ; printnstr
- ;
- ; *** Variables ***
- ; Used to store formatted hex values just before printing it.
- .equ STDIO_HEX_FMT STDIO_RAMSTART
- .equ STDIO_RAMEND @+2
-
- ; *** Code ***
- ; Format the lower nibble of A into a hex char and stores the result in A.
- fmtHex:
- ; The idea here is that there's 7 characters between '9' and 'A'
- ; in the ASCII table, and so we add 7 if the digit is >9.
- ; daa is designed for using Binary Coded Decimal format, where each
- ; nibble represents a single base 10 digit. If a nibble has a value >9,
- ; it adds 6 to that nibble, carrying to the next nibble and bringing the
- ; value back between 0-9. This gives us 6 of that 7 we needed to add, so
- ; then we just condtionally set the carry and add that carry, along with
- ; a number that maps 0 to '0'. We also need the upper nibble to be a
- ; set value, and have the N, C and H flags clear.
- or 0xf0
- daa ; now a =0x50 + the original value + 0x06 if >= 0xfa
- add a, 0xa0 ; cause a carry for the values that were >=0x0a
- adc a, 0x40
- ret
-
- ; Formats value in A into a string hex pair. Stores it in the memory location
- ; that HL points to. Does *not* add a null char at the end.
- fmtHexPair:
- push af
-
- ; let's start with the rightmost char
- inc hl
- call fmtHex
- ld (hl), a
-
- ; and now with the leftmost
- dec hl
- pop af
- push af
- rra \ rra \ rra \ rra
- call fmtHex
- ld (hl), a
-
- pop af
- ret
-
- ; Print the hex char in A
- printHex:
- push bc
- push hl
- ld hl, STDIO_HEX_FMT
- call fmtHexPair
- ld b, 2
- call printnstr
- pop hl
- pop bc
- ret
-
- ; Print the hex pair in HL
- printHexPair:
- push af
- ld a, h
- call printHex
- ld a, l
- call printHex
- pop af
- ret
-
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