> vec() is a bit squirrelly. In a nutshell (heh), vec views its first > argument as a stream of bits taken from the string. The third > argument tells how many bits form a chunk. 8 bits gives chunks that > can each have values from 0 to 255. The second argument tells *which* > chunk, numbering the chunks starting at 0.
so basically a bit twiddling on strings function ? :) > > Probably the weirdest part of vec() is that it can be used both to get > values, and set values (it's one of the four "lvalue" Perl functions). > > So the quoted statement is looking at the scalar $output as a series > of 8-bit chunks - essentially each character of the string. And at > the byte numbered length($output), which would be the byte just after > the current end of the string, we're sticking a new 8-bit value. This > value is coming from computing the ascii value for the letter "E", > which from memory is probably 68 or so. > > In other words, that's just $output .= "E", the very hard way. how about performance? i imagine vec() would be very fast for these operations. > > vec() is really good for a "boolean" array. If you take the string > 1 bit at a time, you can represent 0/1 or false/true with 1 bit > per bit in the string. vec($data, $n, 1) = 1 sets bit $n to 1, > and vec($data, $n, 0) = 0 clears that bit. i have seen this kind of thing done before. maybe i need to just start using it. > > vec() was added when Larry was thinking about what it would take to > rewrite rn in Perl for Perl3. He needed a way to hold the "already > seen" article numbers for a newsgroup, and a simple array holding > numbers into the 100,000s would have been far too fat and wasteful. > > Hmm. Maybe I need to do a column on this. There might be some cool > things there with the bit-ops as well. that would be marvelous. -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
