50 lines
1.1 KiB
ArmAsm
50 lines
1.1 KiB
ArmAsm
.define Cii
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! This subroutine converts integers to integers.
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! Convertions of integers with the same source size as destination
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! size aren't done, there just return the source.
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! A convertion from 4 bytes to 2 bytes just strips the two
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! most significant bytes.
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! A convertion from 2 bytes to 4 bytes tests the sign of the
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! source so that sign extentension takes place if neccesairy.
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Cii:
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cpx #2
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beq Cii_2 ! a conversion from ? to 2
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jsr Pop ! a conversion from 4 to ?
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cpx #4
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beq 8f ! a conversion 4 to 4 (skip)
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jsr Pop
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tay ! save A for sign test
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pha ! save A
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txa
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pha ! save X
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tya ! test on negative
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bmi 1f ! negative means sign extension
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lda #0 ! no sign extension here
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tax
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beq 2f
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1: lda #0FFh ! sign extension here
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tax
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2: jsr Push ! push twobyte integer
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pla
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tax ! get X
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pla ! get A
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jmp Push
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Cii_2: ! a conversion from 2 to ?
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jsr Pop
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cpx #2
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beq 8f ! a conversion from 2 to 2 (skip)
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jsr Pop ! a conversion from 4 to 2
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pha ! save A
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txa
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pha ! save X
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jsr Pop ! strip most significant bytes
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pla ! get X
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tax
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pla ! get A
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jmp Push ! push result
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8: rts
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