Category : Network Files
Archive   : TCP_SRC.ZIP
Filename : MOVEMEM.ASM

;put into the public domain by Russell Nelson, [email protected]

;movemem has one of three values: movemem_test, movemem_386, movemem_86.
;it's initialized to the first, and the code that it points to changes
;it to the appropriate move routine.

movemem dw movemem_test

movemem_test:
pushf
pop ax
or ax,7000h ;the 386 lets us set these bits
push ax
popf
pushf
pop ax
test ax,7000h ;did the bits get set?
mov ax,offset movemem_86
je movemem_test_1 ;no.
mov ax,offset movemem_386 ;yes, use a 386-optimized move.
movemem_test_1:
mov cs:movemem,ax
jmp ax

movemem_386:
movemem_86:
;does the same thing as "rep movsb", only 50% faster.
;moves words instead of bytes, and handles the case of both addresses odd
;efficiently. There is no way to handle one address odd efficiently.
;This routine always aligns the source address in the hopes that the
;destination address will also get aligned. This is from Phil Karn's
;code from ec.c, a part of his NET package. I bummed a few instructions
;out.
jcxz movemem_cnte ; If zero, we're done already.
test si,1 ; Does source start on odd byte?
jz movemem_adre ; Go if not
movsb ; Yes, move the first byte
dec cx ; Count that byte
movemem_adre:
shr cx,1 ; convert to word count
rep movsw ; Move the bulk as words
jnc movemem_cnte ; Go if the count was even
movsb ; Move leftover last byte
movemem_cnte:
ret