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;
; This file, instead of "common/memset.s", will be assembled for the pce
; target. This version is smaller and faster because it uses a HuC6280
; block-copy instruction.
;
; 1998-05-29, Ullrich von Bassewitz
; 2015-11-06, Greg King
;
; void* __fastcall__ _bzero (void* ptr, size_t n);
; void __fastcall__ bzero (void* ptr, size_t n);
; void* __fastcall__ memset (void* ptr, int c, size_t n);
;
; NOTE: bzero() will return its first argument, as memset() does. It is no
; problem to declare the return value as void, because it can be ignored.
; _bzero() (note the leading underscore) is declared with the proper
; return type because the compiler will replace memset() by _bzero() if
; the fill value is zero; and, the optimizer looks at the return type
; to see if the value in .XA is of any use.
;
; NOTE: This function uses entry points from "pce/memcpy.s"!
;
.export __bzero, _bzero, _memset
.import memcpy_getparams, memcpy_increment
.import pushax, popax
.importzp ptr1, ptr2, ptr3
.macpack longbranch
; ----------------------------------------------------------------------
__bzero:
_bzero: pha
cla ; fill with zeros
jsr pushax ; (high byte isn't important)
pla
_memset:
jsr memcpy_getparams
; The fill byte is put at the beginning of the buffer; then, the buffer is
; copied to a second buffer that starts one byte above the start of the first
; buffer. Normally, we would use memmove() to avoid trouble; but here, we
; exploit that overlap, by using memcpy(). Therefore, the fill value is copied
; from each byte to the next byte, all the way to the end of the buffer.
lda ptr1 ; get fill value
sta (ptr2)
lda ptr3 ; count first byte
bne @L3
dec ptr3+1
@L3: dec a
sta ptr3
ora ptr3+1
jeq popax ; return ptr. if no more bytes
lda ptr2 ; point to first buffer
ldx ptr2+1
sta ptr1
stx ptr1+1
inc ptr2 ; point to second buffer
bne @L2
inc ptr2+1
@L2: jmp memcpy_increment
|
