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The Elegance of the ASCII Table

danq.me

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Re: The Elegance of the ASCII Table

#7

Post by mananaysiempre »

lucasoshiro wrote: post #2

Once I saw a case-insensitive switch in C using that pattern of letters: switch (my_char | 0x20) { case 'a': ... break; case 'b': ... break; }

This can be made to work for ASCII and EBCDIC simultaneously for extra esoterica points:

  switch (my_char | 'A' ^ 'a') {
  case 'A' | 'a': /* ... */ break;
  /* ... */
  }
I don’t know if this is too fancy to have ever made it into real code, but I believe I’ve seen places in the ICU source that still say ('A' <= x <= 'I' || 'J' <= x <= 'R' || 'S <= x <= 'Z') instead of just ('A' <= x <= 'Z'), EBCDIC letters being arranged in those three contiguous ranges.

Re: The Elegance of the ASCII Table

#8

Post by ggm » 

  man ascii
is never far from my fingers. combined with od -c and od -x it gets the job done. I don't think as fluently in Octal as I used to. Hex has become ubiquitous.

Re: The Elegance of the ASCII Table

#9

Post by transfire »

One downside of ASCII is the lack of two extra “letters” (whatever they might be, e.g. perhaps German ß), as it makes it impossible to represent base 64 alphanumerically. So we ended up with many alternatives picking two arbitrary punctuation marks.

Re: The Elegance of the ASCII Table

#10

Post by jolmg »

> So when you’re reading 7-bit ASCII, if it starts with 00, it’s a non-printing character. Otherwise it’s a printing character.

> The first printing character is space; it’s an invisible character, but it’s still one that has meaning to humans, so it’s not a control character (this sounds obvious today, but it was actually the source of some semantic argument when the ASCII standard was first being discussed).

Hmm.. Interesting that space is considered a printing character while horizontal tab and newline are control characters. They're all invisible and move the cursor, but I guess it makes sense. Space is uniquely very specific in how the cursor is moved one character space, so it's like an invisible character. Newline can either imply movement straight down, or down and to the left, depending on a configuration or platform (e.g. DOS vs UNIX line endings). Horizontal tab can also move you a configurable amount rightwards, and perhaps it might've been thought a bit differently, given there's also a vertical tab, which I've got no idea on how it was used. Maybe it's the newline-equivalent for tables, e.g. "id\tcolor\v1\tred\v2\tblue\v" or something like that.

Interesting also that BS is a control char while DEL is a printing(?) char. I guess that's because BS implies just movement leftwards over the text, while DEL is all ones like running a black sharpie through text. Guess that's what makes it printing. Wonder if there were DEL keys on typewriters that just stamped a black square, and on keypunchers that just punched 7 holes, so people would press "backspace" to go back then "delete" to overwrite.

I've used ASCII a lot, but even after so many years, I'm getting moments where it's like "oh this piece isn't just here, it needs to be here for a deep reason". It's like a jigsaw puzzle.

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