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;
; void* __fastcall__ memset (void* ptr, int c, size_t n);
; void* __fastcall__ _bzero (void* ptr, size_t n);
; void __fastcall__ bzero (void* ptr, size_t n);
;
; Ullrich von Bassewitz, 29.05.1998
; Performance increase (about 20%) by
; Christian Krueger, 12.09.2009, slightly improved 12.01.2011
;
; NOTE: bzero will return it's first argument as memset does. It is no problem
; to declare the return value as void, since it may 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 a/x is of any use.
;
.export _memset, _bzero, __bzero
.import popax
.importzp sp, ptr1, ptr2, ptr3
_bzero:
__bzero:
sta ptr3
stx ptr3+1 ; Save n
ldx #0 ; Fill with zeros
beq common
_memset:
sta ptr3 ; Save n
stx ptr3+1
jsr popax ; Get c
tax
; Common stuff for memset and bzero from here
common: ; Fill value is in X!
ldy #1
lda (sp),y
sta ptr1+1 ; save high byte of ptr
dey ; Y = 0
lda (sp),y ; Get ptr
sta ptr1
lsr ptr3+1 ; divide number of
ror ptr3 ; bytes by two to increase
bcc evenCount ; speed (ptr3 = ptr3/2)
oddCount:
; y is still 0 here
txa ; restore fill value
sta (ptr1),y ; save value and increase
inc ptr1 ; dest. pointer
bne evenCount
inc ptr1+1
evenCount:
lda ptr1 ; build second pointer section
clc
adc ptr3 ; ptr2 = ptr1 + (length/2) <- ptr3
sta ptr2
lda ptr1+1
adc ptr3+1
sta ptr2+1
txa ; restore fill value
ldx ptr3+1 ; Get high byte of n
beq L2 ; Jump if zero
; Set 256/512 byte blocks
; y is still 0 here
L1: .repeat 2 ; Unroll this a bit to make it faster
sta (ptr1),y ; Set byte in lower section
sta (ptr2),y ; Set byte in upper section
iny
.endrepeat
bne L1
inc ptr1+1
inc ptr2+1
dex ; Next 256 byte block
bne L1 ; Repeat if any
; Set the remaining bytes if any
L2: ldy ptr3 ; Get the low byte of n
beq leave ; something to set? No -> leave
L3: dey
sta (ptr1),y ; set bytes in low
sta (ptr2),y ; and high section
bne L3 ; flags still up to date from dey!
leave:
jmp popax ; Pop ptr and return as result
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