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53 lines
1.2 KiB
ArmAsm
53 lines
1.2 KiB
ArmAsm
;
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; Ullrich von Bassewitz, 31.05.1998
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; Christian Krueger, 2013-Aug-04, minor optimization
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;
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; const char* strchr (const char* s, int c);
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;
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.export _strchr
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.import popax
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.importzp ptr1, tmp1
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.macpack cpu
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_strchr:
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sta tmp1 ; Save c
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jsr popax ; get s
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tay ; low byte of pointer to y
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stx ptr1+1
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.if (.cpu .bitand ::CPU_ISET_65SC02)
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stz ptr1
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.else
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lda #0
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sta ptr1 ; access from page start, y contains low byte
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.endif
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Loop: lda (ptr1),y ; Get next char
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beq EOS ; Jump on end of string
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cmp tmp1 ; Found?
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beq Found ; Jump if yes
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iny
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bne Loop
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inc ptr1+1
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bne Loop ; Branch always
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; End of string. Check if we're searching for the terminating zero
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EOS:
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lda tmp1 ; Get the char we're searching for
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bne NotFound ; Jump if not searching for terminator
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; Found. Set pointer to c.
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Found:
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ldx ptr1+1 ; Load high byte of pointer
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tya ; low byte is in y
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rts
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; Not found, return NULL
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NotFound:
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lda #0
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tax
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rts
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