76 lines
1.6 KiB
ArmAsm
76 lines
1.6 KiB
ArmAsm
.define .mli4
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! 32-bit multiply routine for z80
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! parameters:
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! on stack
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! register utilization:
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! ix: least significant 2 bytes of result
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! hl: most significant 2 bytes of result
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! bc: least significant 2 bytes of multiplicand
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! de: most significant 2 bytes of multiplicand
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! iy: 2 bytes of multiplier (first most significant,
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! later least significant)
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! a: bit count
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.mli4:
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!initialization
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pop hl ! return address
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pop de
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ld (.mplier+2),de! least significant bytes of
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! multiplier
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pop de
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ld (.mplier),de ! most sign. bytes
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pop de ! least significant bytes of
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! multiplicand
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pop bc ! most sign. bytes
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push hl ! return address
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push iy ! LB
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ld ix,0
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xor a
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ld h,a ! clear result
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ld l,a
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ld (.flag),a ! indicate that this is
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! first pass of main loop
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ld iy,(.mplier)
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! main loop, done twice, once for each part (2 bytes)
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! of multiplier
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1:
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ld a,16
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! sub-loop, done 16 times
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2:
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add iy,iy ! shift left multiplier
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jr nc,3f ! skip if most sign. bit is 0
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add ix,de ! 32-bit add
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adc hl,bc
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3:
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dec a
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jr z,4f ! done with this part of multiplier
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add ix,ix ! 32-bit shift left
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adc hl,hl
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jr 2b
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4:
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! see if we have just processed the first part
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! of the multiplier (flag = 0) or the second
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! part (flag = 1)
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ld a,(.flag)
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or a
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jr nz,5f
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inc a ! a := 1
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ld (.flag),a ! set flag
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ld iy,(.mplier+2)! least significant 2 bytes now in iy
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add ix,ix ! 32-bit shift left
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adc hl,hl
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jr 1b
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5:
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! clean up
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pop iy ! restore LB
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ex (sp),hl ! put most sign. 2 bytes of result
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! on stack; put return address in hl
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push ix ! least sign. 2 bytes of result
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jp (hl) ! return
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.data
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.flag: .byte 0
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.mplier: .space 4
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