On Thu, 7 Mar 2002, Siders, Keith wrote:
> You can get that down to 5 instructions. You could either use a typecast, or
> for portability, use a union definition. For that matter you could even
> typecast *mptr as a pointer to the union and extract the data from the
> string however you choose. But it still takes 5 instructions, unless you're
> pulling the data into another buffer, in which case you're down to 4.
Which 5 instructions are those? For htonl from memory, the only sequence
I can think of is the "obvious" one of lbu/shift (7 instructions). And
for swapping BE-LE in memory (an important thing for me), I do not see any
method better than the "obvious" one I mentioned earlier:
90c50000 lbu a1,0(a2)
90c40001 lbu a0,1(a2)
90c30002 lbu v1,2(a2)
90c20003 lbu v0,3(a2)
a0c20000 sb v0,0(a2)
a0c30001 sb v1,1(a2)
a0c40002 sb a0,2(a2)
a0c50003 sb a1,3(a2)
Thanks,
-Richard
> -> From: Richard Hodges [mailto:rh@matriplex.com]
> -> To me, byte swapping on MIPS actually seems rather
> -> expensive. The code
> -> for htonl (linux/byteorder/swab.h) ends up something like this:
> ->
> -> srl $5,$4,8
> -> andi $5,$5,0xff00
> -> srl $2,$4,24
> -> andi $3,$4,0xff00
> -> or $2,$2,$5
> -> sll $3,$3,8
> -> or $2,$2,$3
> -> sll $4,$4,24
