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