144 lines
3 KiB
ArmAsm
144 lines
3 KiB
ArmAsm
.define .cii
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.define .cuu
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.sect .text
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.sect .rom
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.sect .data
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.sect .bss
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.sect .text
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! cii: convert integer to integer
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! parameters:
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! stack: destination size
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! source size
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! source
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! stack: result (out)
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! This code is also used by cuu.
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! The contents of the a-register determines
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! if we're doing a cii (a=0) or a cuu (a=1),
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! so be very careful with this register!
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.cii:
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pop ix ! return address
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pop hl ! destination size
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pop de ! source size
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ld b,h ! bc := destination size
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ld c,l
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xor a ! watch it, this is dirty!
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! Besides clearing the carry
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! this instruction sets a-reg.
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! to 0, to indicate this is
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! a cii and not a cuu.
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sbc hl,de ! hl := destination size
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! - source size
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jr z,1f ! equal, return
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jp p,2f ! larger, expand
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! smaller, shrink
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! The most significant part of the source
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! is removed. As the least sign. part is
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! on top of the stack, we have to move an
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! entire data block.
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9:
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add hl,sp ! note that hl < 0
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! (also come here via cuu)
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add hl,de
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dec hl ! now hl points to most
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! significant byte of what
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! will be left over of source
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ex de,hl
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add hl,sp
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ex de,hl
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dec de ! now de points to highest
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! byte of source
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lddr ! move 'destination size'
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! bytes upwards (i.e. away
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! from top of stack)
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inc de
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ex de,hl
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ld sp,hl ! adjust stackpointer
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1:
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jp (ix) ! return
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2:
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! larger, expand
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! A number of bytes (containing the signbits
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! of the source) is inserted before the most
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! significant byte of the source.
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! As this byte is somewhere in the middle of
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! the stack, the entire source must first be
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! moved downwards (in the direction of the
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! top)
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8:
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ld b,d ! bc := source size
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! (also come here via cuu)
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ld c,e
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ex de,hl ! de := difference (> 0)
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ld hl,0
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add hl,sp ! hl := sp
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push hl
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or a
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sbc hl,de
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ex de,hl ! de := sp - difference
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pop hl ! hl := sp
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ex de,hl ! adjust sp
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ld sp,hl
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ex de,hl
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ldir ! move source upwards,
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! creating a 'hole'
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! inside the stack
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! now we will fill the hole with bytes
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! containing either 0 or -1, depending
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! on the signbit of the source.
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or a
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sbc hl,de
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ex de,hl ! de := difference
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dec hl ! now hl points to
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! most significant byte
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! of the source
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or a ! see if we're doing
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! a 'cii' or a 'cuu'
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jr nz,3f ! cuu, expand with zeroes
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bit 7,(hl) ! test signbit
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jr z,3f
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dec b ! b := -1 (was 0 after ldir)
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3:
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inc hl
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ld (hl),b ! either 0 or -1
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dec de
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ld a,d
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or e
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jr nz,3b
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jp (ix) ! return
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! cuu: convert unsigned to unsigned
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! parameters:
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! stack: destination size
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! source size
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! source
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! stack: result (out)
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! The only difference between a cuu and a cii is:
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! if the destination is larger than the source,
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! the former extends with zeroes and the latter
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! extends with sign bits
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! cuu uses the code of cii. In this case it puts
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! a '1' in the accumulator to indicate this is
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! a cuu.
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.cuu:
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pop ix
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pop hl
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pop de
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ld b,h
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ld c,l
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xor a ! clear carry
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sbc hl,de
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jr z,1b ! equal, return
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jp m,9b ! smaller, shrink
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inc a ! a := 1
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jr 8b ! larger, expand
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