A faster ASCII table

This is a discussion on A faster ASCII table within the Tech Board forums, part of the Community Boards category; I just came up with a faster version of ASCII on the subway this morning... Since string parsing usually does ...

  1. #1
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    A faster ASCII table

    I just came up with a faster version of ASCII on the subway this morning...
    Since string parsing usually does a lot of changing case or case-insensitive comparisons, wouldn't it have been better if small and capital letters would have been exactly the same bits except for something like the highest bit? That way if you want to convert between upper & lower case, all you need to do is flip a bit instead of having an if statement check if the char value is > x && < y...
    I know it probably wouldn't make a huge performance impact, but every little bit helps.
    Now I just need a DeLorean so I can go back in time and change the ASCII table...
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

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    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by cpjust View Post
    I just came up with a faster version of ASCII on the subway this morning...
    Since string parsing usually does a lot of changing case or case-insensitive comparisons, wouldn't it have been better if small and capital letters would have been exactly the same bits except for something like the highest bit? That way if you want to convert between upper & lower case, all you need to do is flip a bit instead of having an if statement check if the char value is > x && < y...
    I know it probably wouldn't make a huge performance impact, but every little bit helps.
    Now I just need a DeLorean so I can go back in time and change the ASCII table...
    Is this some sort of obscure joke? (Upper and lowercase letters differ by exactly one bit in ASCII.)

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    Captain Crash brewbuck's Avatar
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    Code:
    unsigned char FlipCase( unsigned char ch )
    {
        return ch ^ 0x20;
    }
    Already works.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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    Registered User jdragyn's Avatar
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    Apparently you already went back in time.
    C+/- programmer extraordinaire

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    Woof, woof! zacs7's Avatar
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    Perhaps he means... "even faster."

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    (?<!re)tired Mario F.'s Avatar
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    I actually didn't ever noticed they differed by one bit. Cool!
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

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    spurious conceit MK27's Avatar
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    Quote Originally Posted by Mario F. View Post
    I actually didn't ever noticed they differed by one bit. Cool!
    Me either. I just thot it was neat that they differ by exactly 32, which is the value of the SPACE!!! Is that really 0x20 in hex????!?

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    Shrug...

    Actually, ASCII has been tremendously well thought of IMHO. Not just that, but it has all kinds of patterns when you look closely. You know, for instance, that for digits 0-9, the least significant 4 bits represents the value? And, yes, that matching characters usually differ by only one bit.

    I wish unicode was like that, though, where you can easily determine if a character has an upper/lower case variant and convert it in one bit. The latter is probably usually possible, but the former, afaik, requires lookup tables.

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    Jack of many languages Dino's Avatar
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    EBCDIC does this too. The X'40' bit (aka, the blank).
    Mac and Windows cross platform programmer. Ruby lover.

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    Amen brother!

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    Quote Originally Posted by brewbuck View Post
    Code:
    unsigned char FlipCase( unsigned char ch )
    {
        return ch ^ 0x20;
    }
    Already works.
    Sure, but what if the character isn't a letter? If it's a number or punctuation, that won't work.
    I was thinking of something like 0 - 127 being the same as 128 - 255 except for upper case letters. That way you won't have to look at whether the char is a letter or something else, you just flip the highest bit.
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

    "the internet is a scary place to be thats why i dont use it much." - billet, 03/17/2010

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    Quote Originally Posted by cpjust View Post
    Sure, but what if the character isn't a letter? If it's a number or punctuation, that won't work.
    I was thinking of something like 0 - 127 being the same as 128 - 255 except for upper case letters. That way you won't have to look at whether the char is a letter or something else, you just flip the highest bit.
    And with this change you've just reduced the ascii table from 256 characters to 154

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    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by _Mike View Post
    And with this change you've just reduced the ascii table from 256 characters to 154
    The ASCII set was only 128 characters to begin with.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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    Quote Originally Posted by brewbuck View Post
    The ASCII set was only 128 characters to begin with.
    Yes but I assumed he was refering to the 8 bit extended table. His suggestion would not even fit in a 7 bit table.

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    That is a neat function brewbuck, I'll use that.

  15. #15
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    Quote Originally Posted by _Mike View Post
    And with this change you've just reduced the ascii table from 256 characters to 154
    Where did the 154 come from? 256 / 2 = 128.

    Quote Originally Posted by _Mike View Post
    Yes but I assumed he was refering to the 8 bit extended table. His suggestion would not even fit in a 7 bit table.
    I was talking about an 8-bit byte, of which ASCII only defines 7 bits, so you've already got a free bit to play with, so why not make use of it?
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

    "the internet is a scary place to be thats why i dont use it much." - billet, 03/17/2010

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