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[REBOL] Re: bitset actions?

From: brett:codeconscious at: 10-Oct-2003 16:36

Hi Rebolinth, I am not sure about what you are trying to achieve, but I think you may have the wrong idea about bitsets. Here are some examples to help you. Bitsets are not series:
>> series? make bitset! 8
== false However they do have a length - the number of bits (always a multiple of 8):
>> length? make bitset! 8
== 8
>> length? make bitset! 16
== 16 The Charset function just creates bitsets from the character you specify:
>> source charset
charset: func [ "Makes a bitset of chars for the parse function." chars [string! block!] ][ make bitset! chars ] The number of bits in a bitset created by the Charset function is (currently) 256 - one bit to represent each possible character:
>> length? charset ""
== 256 With bitsets you are *only* turning some bits on and some bits off by a position number. Characters are translated to a position.
> Is there a way to 'pick on bitsets?
You use Find to test if a bit corresponding to your value is set:
>> find charset "ab" "a"
== true
>> find charset "ab" "b"
== true
>> find charset "ab" "c"
== none You can use the ascii value:
>> find charset "*" 42
== true You can set bits corresponding to your value with Insert:
>> find insert charset "ab" "d" "d"
== true To enumerate all the characters represented in a bitset created using charset use a loop (notice also that the bitset does not record duplicates): bitset: charset "aaaaybcx" chars: copy {} for i 0 (subtract length? bitset 1) 1 [ if find bitset i [append chars to-char i] ] ?? chars When using Parse bitsets can be used for matching against a set of characters: my-chars: charset "xyz" is simpler and probably more efficient than my-chars: [#"x" | #"y" | #"z"] You can use bitsets with Find too:
>> find "123x5" charset "xyz"
== "x5" Clear, Empty?, Union, Interset, Exclude, Difference, Negate and Complement can be used on bitsets Example using just a small bitset.
>> find insert make bitset! 8 6 6
== true Outside the range:
>> insert make bitset! 8 9
** Script Error: Invalid argument: 9 ** Near: insert make bitset! 8 9
>> find make bitset! 8 9
** Script Error: Invalid argument: 9 ** Near: find make bitset! 8 9 Cheers, Brett.