; Fill B bytes at (HL) with A
fill:
push bc
push hl
loop:
ld (hl), a
inc hl
djnz .loop
pop hl
pop bc
ret
; Increase HL until the memory address it points to is equal to A for a maximum
; of 0xff bytes. Returns the new HL value as well as the number of bytes
; iterated in A.
; If a null char is encountered before we find A, processing is stopped in the
; same way as if we found our char (so, we look for A *or* 0)
; Set Z if the character is found. Unsets it if not
findchar:
push bc
ld c, a ; let's use C as our cp target
ld b, 0xff
loop: ld a, (hl)
cp c
jr z, .match
or a ; cp 0
jr z, .nomatch
inc hl
djnz .loop
nomatch:
inc a ; unset Z
jr .end
match:
; We ran 0xff-B loops. That's the result that goes in A.
ld a, 0xff
sub b
cp a ; ensure Z
end:
pop bc
ret
; Compares strings pointed to by HL and DE up to A count of characters. If
; equal, Z is set. If not equal, Z is reset.
strncmp:
push bc
push hl
push de
ld b, a
loop:
ld a, (de)
cp (hl)
jr nz, .end ; not equal? break early. NZ is carried out
; to the called
cp 0 ; If our chars are null, stop the cmp
jr z, .end ; The positive result will be carried to the
; caller
inc hl
inc de
djnz .loop
; We went through all chars with success, but our current Z flag is
; unset because of the cp 0. Let's do a dummy CP to set the Z flag.
cp a
end:
pop de
pop hl
pop bc
; Because we don't call anything else than CP that modify the Z flag,
; our Z value will be that of the last cp (reset if we broke the loop
; early, set otherwise)
ret
; Transforms the character in A, if it's in the a-z range, into its upcase
; version.
upcase:
cp 'a'
ret c ; A < 'a'. nothing to do
cp 'z'+1
ret nc ; A >= 'z'+1. nothing to do
; 'a' - 'A' == 0x20
sub 0x20
ret
