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73 lines
1.7 KiB
ArmAsm
73 lines
1.7 KiB
ArmAsm
;
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; Ullrich von Bassewitz, 15.09.2000
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;
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; int memcmp (const void* p1, const void* p2, size_t count);
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;
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.export _memcmp
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.import popax, return0
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.importzp ptr1, ptr2, ptr3
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_memcmp:
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; Calculate (-count-1) and store it into ptr3. This is some overhead here but
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; saves time in the compare loop
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eor #$FF
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sta ptr3
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txa
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eor #$FF
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sta ptr3+1
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; Get the pointer parameters
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jsr popax ; Get p2
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sta ptr2
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stx ptr2+1
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jsr popax ; Get p1
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sta ptr1
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stx ptr1+1
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; Loop initialization
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ldx ptr3 ; Load low counter byte into X
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ldy #$00 ; Initialize pointer
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; Head of compare loop: Test for the end condition
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Loop: inx ; Bump low byte of (-count-1)
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beq BumpHiCnt ; Jump on overflow
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; Do the compare
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Comp: lda (ptr1),y
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cmp (ptr2),y
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bne NotEqual ; Jump if bytes not equal
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; Bump the pointers
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iny ; Increment pointer
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bne Loop
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inc ptr1+1 ; Increment high bytes
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inc ptr2+1
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bne Loop ; Branch always (pointer wrap is illegal)
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; Entry on low counter byte overflow
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BumpHiCnt:
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inc ptr3+1 ; Bump high byte of (-count-1)
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bne Comp ; Jump if not done
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jmp return0 ; Count is zero, areas are identical
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; Not equal, check which one is greater
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NotEqual:
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bcs Greater
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ldx #$FF ; Make result negative
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rts
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Greater:
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ldx #$01 ; Make result positive
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rts
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