51 lines
812 B
ArmAsm
51 lines
812 B
ArmAsm
.define .mlu2
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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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! 16 bits unsigned multiply routine
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! Expects operands on stack
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! Yields result in de-registers
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! This routine could also be used for signed integers, but it won't
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! because there is a more clever one just for signed integers.
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.mlu2:
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pop h
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shld .retadr
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mov h,b
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mov l,c
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shld .bcreg
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pop b ! bc = multiplier
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pop d ! de = multiplicand
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lxi h,0 ! hl = product
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1: mov a,b ! if multiplier = 0 then finished
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ora c
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jz 3f
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xra a ! reset carry
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mov a,b ! shift multiplier right
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rar
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mov b,a
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mov a,c
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rar
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mov c,a
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jnc 2f !if carry set: add multiplicand to product
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dad d
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2: xchg ! shift multiplicand left
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dad h
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xchg
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jmp 1b ! keep looping
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3: xchg ! de becomes product
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lhld .bcreg
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mov b,h
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mov c,l
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lhld .retadr
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pchl
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