mirror of
https://github.com/hsoft/collapseos.git
synced 2024-11-30 22:08:08 +11:00
64 lines
1.5 KiB
NASM
64 lines
1.5 KiB
NASM
|
; Parse the hex char at A and extract it's 0-15 numerical value. Put the result
|
||
|
|
; in A.
|
||
|
|
;
|
||
|
|
; On success, the carry flag is reset. On error, it is set.
|
||
|
|
parseHex:
|
||
|
|
; First, let's see if we have an easy 0-9 case
|
||
|
|
cp '0'
|
||
|
|
jr c, .error ; if < '0', we have a problem
|
||
|
|
cp '9'+1
|
||
|
|
jr nc, .alpha ; if >= '9'+1, we might have alpha
|
||
|
|
; We are in the 0-9 range
|
||
|
|
sub '0' ; C is clear
|
||
|
|
ret
|
||
|
|
|
||
|
|
.alpha:
|
||
|
|
call upcase
|
||
|
|
cp 'A'
|
||
|
|
jr c, .error ; if < 'A', we have a problem
|
||
|
|
cp 'F'+1
|
||
|
|
jr nc, .error ; if >= 'F', we have a problem
|
||
|
|
; We have alpha.
|
||
|
|
sub 'A'-10 ; C is clear
|
||
|
|
ret
|
||
|
|
|
||
|
|
.error:
|
||
|
|
scf
|
||
|
|
ret
|
||
|
|
|
||
|
|
; Parses 2 characters of the string pointed to by HL and returns the numerical
|
||
|
|
; value in A. If the second character is a "special" character (<0x21) we don't
|
||
|
|
; error out: the result will be the one from the first char only.
|
||
|
|
; HL is set to point to the last char of the pair.
|
||
|
|
;
|
||
|
|
; On success, the carry flag is reset. On error, it is set.
|
||
|
|
parseHexPair:
|
||
|
|
push bc
|
||
|
|
|
||
|
|
ld a, (hl)
|
||
|
|
call parseHex
|
||
|
|
jr c, .end ; error? goto end, keeping the C flag on
|
||
|
|
rla \ rla \ rla \ rla ; let's push this in MSB
|
||
|
|
ld b, a
|
||
|
|
inc hl
|
||
|
|
ld a, (hl)
|
||
|
|
cp 0x21
|
||
|
|
jr c, .single ; special char? single digit
|
||
|
|
call parseHex
|
||
|
|
jr c, .end ; error?
|
||
|
|
or b ; join left-shifted + new. we're done!
|
||
|
|
; C flag was set on parseHex and is necessarily clear at this point
|
||
|
|
jr .end
|
||
|
|
|
||
|
|
.single:
|
||
|
|
; If we have a single digit, our result is already stored in B, but
|
||
|
|
; we have to right-shift it back.
|
||
|
|
ld a, b
|
||
|
|
and 0xf0
|
||
|
|
rra \ rra \ rra \ rra
|
||
|
|
dec hl
|
||
|
|
|
||
|
|
.end:
|
||
|
|
pop bc
|
||
|
|
ret
|