Efficient bitwise operations
Fri Jun 20 11:52:15 CEST 2003
You can treat each byte as an integer and do
bsl - bit shift left
bsr - bit shift right
These operators are described in the first chapter of the red book.
11> 1 bsl 1.
12> 1 bsl 2.
13> 4 bsr 1.
14> 4 bsr 2.
To swap nibbles
((Int band 15) bsl 4) + ((Int band 240) bsr 4).
From: Rudolph van Graan [mailto:rvg@REDACTED]
Sent: 20 June 2003 09:34
Subject: Efficient bitwise operations
Hi there again,
Thanks again for all the answers previously - helped me a lot!
I've had to write some bitwise operations yesterday, because I couldn't
locate any bifs or operations that do the same:
Bitwise roll left:
rroll(<<Byte>>,Rolls) when Rolls > 0 ->
Output = rroll1(<<Byte>>),
Bitwise roll right:
lroll(<<Byte>>,Rolls) when Rolls > 0 ->
Output = lroll1(<<Byte>>),
Bitwise high <-> low nibble swap:
My question here has to do with the efficiency of the above code.
Normally, I would have used a single assembly instruction to achieve the
same result, but even though the code works, how efficient can it really
be? Are there any obvious things I've missed in the documentation?
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