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82 lines
1.6 KiB
ArmAsm
82 lines
1.6 KiB
ArmAsm
;
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; Ullrich von Bassewitz, 25.05.2000
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;
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; int strncmp (const char* s1, const char* s2, unsigned n);
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;
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.export _strncmp
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.import popax
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.importzp ptr1, ptr2, ptr3
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_strncmp:
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; Convert the given counter value in a/x from a downward counter into an
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; upward counter, so we can increment the counter in the loop below instead
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; of decrementing it. This adds some overhead now, but is cheaper than
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; executing a more complex test in each iteration of the loop. We do also
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; correct the value by one, so we can do the test on top of the 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 remaining arguments
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jsr popax ; get s2
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sta ptr2
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stx ptr2+1
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jsr popax ; get s1
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sta ptr1
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stx ptr1+1
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; Loop setup
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ldy #0
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; Start of compare loop. Check the counter.
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Loop: inc ptr3
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beq IncHi ; Increment high byte
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; Compare a byte from the strings
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Comp: lda (ptr1),y
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cmp (ptr2),y
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bne NotEqual ; Jump if strings different
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tax ; End of strings?
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beq Equal1 ; Jump if EOS reached, a/x == 0
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; Increment the pointers
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iny
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bne Loop
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inc ptr1+1
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inc ptr2+1
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bne Loop ; Branch always
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; Increment hi byte
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IncHi: inc ptr3+1
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bne Comp ; Jump if counter not zero
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; Exit code if strings are equal. a/x not set
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Equal: lda #$00
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tax
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Equal1: rts
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; Exit code if strings not equal
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NotEqual:
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bcs L1
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ldx #$FF ; Make result negative
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rts
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L1: ldx #$01 ; Make result positive
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rts
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