mirror of
https://github.com/hsoft/collapseos.git
synced 2024-11-08 17:58:05 +11:00
86 lines
2.0 KiB
NASM
86 lines
2.0 KiB
NASM
; core
|
|
;
|
|
; Routines used pretty much all everywhere. Unlike all other kernel units,
|
|
; this unit is designed to be included directly by userspace apps, not accessed
|
|
; through jump tables. The reason for this is that jump tables are a little
|
|
; costly in terms of machine cycles and that these routines are not very costly
|
|
; in terms of binary space.
|
|
; Therefore, this unit has to stay small and tight because it's repeated both
|
|
; in the kernel and in userspace. It should also be exclusively for routines
|
|
; used in the kernel.
|
|
|
|
; add the value of A into DE
|
|
addDE:
|
|
push af
|
|
add a, e
|
|
jr nc, .end ; no carry? skip inc
|
|
inc d
|
|
.end:
|
|
ld e, a
|
|
pop af
|
|
noop: ; piggy backing on the first "ret" we have
|
|
ret
|
|
|
|
; add the value of A into HL
|
|
; affects carry flag according to the 16-bit addition, Z, S and P untouched.
|
|
addHL:
|
|
push de
|
|
ld d, 0
|
|
ld e, a
|
|
add hl, de
|
|
pop de
|
|
ret
|
|
|
|
|
|
; copy (HL) into DE, then exchange the two, utilising the optimised HL instructions.
|
|
; ld must be done little endian, so least significant byte first.
|
|
intoHL:
|
|
push de
|
|
ld e, (hl)
|
|
inc hl
|
|
ld d, (hl)
|
|
ex de, hl
|
|
pop de
|
|
ret
|
|
|
|
intoDE:
|
|
ex de, hl
|
|
call intoHL
|
|
ex de, hl ; de preserved by intoHL, so no push/pop needed
|
|
ret
|
|
|
|
intoIX:
|
|
push ix
|
|
ex (sp), hl ;swap hl with ix, on the stack
|
|
call intoHL
|
|
ex (sp), hl ;restore hl from stack
|
|
pop ix
|
|
ret
|
|
|
|
; Call the method (IX) is a pointer to. In other words, call intoIX before
|
|
; callIX
|
|
callIXI:
|
|
push ix
|
|
call intoIX
|
|
call callIX
|
|
pop ix
|
|
ret
|
|
|
|
; jump to the location pointed to by IX. This allows us to call IX instead of
|
|
; just jumping it. We use IX because we seldom use this for arguments.
|
|
callIX:
|
|
jp (ix)
|
|
|
|
callIY:
|
|
jp (iy)
|
|
|
|
; Ensures that Z is unset (more complicated than it sounds...)
|
|
; There are often better inline alternatives, either replacing rets with
|
|
; appropriate jmps, or if an 8 bit register is known to not be 0, an inc
|
|
; then a dec. If a is nonzero, 'or a' is optimal.
|
|
unsetZ:
|
|
or a ;if a nonzero, Z reset
|
|
ret nz
|
|
cp 1 ;if a is zero, Z reset
|
|
ret
|