Beefy Boxes and Bandwidth Generously Provided by pair Networks
"be consistent"

Re: In-place bitwise NOT?

by Perlbotics (Chancellor)
on Jul 26, 2013 at 18:02 UTC ( #1046576=note: print w/replies, xml ) Need Help??

in reply to In-place bitwise NOT?

I am not sure, if this works as you expect... maybe the macros and wrappers generate a copy under the hood?

use Inline C; use strict; use warnings; my $x = "012\xf0ABC\x0f\x00\x01\xff"; print unpack("H*", $x ), "\n"; # 303132f04142430f0001ff flipbits( $x, length $x ); print unpack("H*", $x ), "\n"; # cfcecd0fbebdbcf0fffe00 __END__ __C__ void flipbits(char* a, int len ) { for ( ; len-- ; ++a ) *a ^= 0xff; }

Update: Switching to 32bit blocks gave a huge improvement on my 32bit setup...

void flipbits32(char* a, int len ) { int blocks = len >> 2; if ( sizeof blocks == 4 ) { /* try 32bit blocks */ for ( ; blocks-- ; a += 4 ) *( (unsigned int*) a ) ^= 0xffffffffU +; /* TODO: add treatment for last 1..3 bytes if len is not a multipl +e of 4 */ } else { /* fallback to 8bit */ for ( ; len-- ; ++a ) *a ^= 0xff; } }
Rate str inline inline32 str 69.1/s -- -37% -69% flipbits 110/s 59% -- -51% flipbits32 223/s 222% 103% --

Potential next steps which are also less general, but that's the price to pay:

Replies are listed 'Best First'.
Re^2: In-place bitwise NOT?
by BrowserUk (Pope) on Jul 26, 2013 at 19:54 UTC

    That certainly works and doesn't appear to do any copying. It comes out at nearly 50% faster than tr//:

    C:\test>1046579 -N=2**20 Rate str translate C str 656/s -- -8% -37% translate 713/s 9% -- -32% C 1047/s 60% 47% --

    The only downside is that it imposes the need for a compiler on a module that otherwise doesn't need one.

    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.

Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://1046576]
and all is quiet...

How do I use this? | Other CB clients
Other Users?
Others drinking their drinks and smoking their pipes about the Monastery: (4)
As of 2017-10-23 03:10 GMT
Find Nodes?
    Voting Booth?
    My fridge is mostly full of:

    Results (276 votes). Check out past polls.