shric4 months ago
A fun read on word count optimization can be found in Abrash's Black Book:
https://www.jagregory.com/abrash-black-book/#lessons-learned...
You can gloss over the asm if you wish, the tricks that are explained around it are worth it imho.
Joker_vD4 months ago
I wonder if large lookup tables/table-driven state machines are still as good as they used to be. After all, even with all the on-chip caches, the additional memory accesses today seem to be slower than doing some multi-instruction SIMD voodoo.
LegionMammal9784 months ago
At least the GNU version of wc [0] uses AVX2 for line counting, if available. Though it falls back to a simple character-by-character loop if you ask for a character count [not to be confused with a byte count!] or a word count.
[0] https://git.savannah.gnu.org/cgit/coreutils.git/tree/src/wc_...
tripdout4 months ago
Those `goto`s between two different for loops is crazy.
actionfromafar4 months ago
Assembly / machine code thinking.
amszmidt4 months ago
More like a relic of (actual) "spaghetti code", it was relatively common in really old Lisp code.
lifthrasiir4 months ago
Not that crazy given that it closely mirrors it's state machine structure.
Joker_vD4 months ago
> A word is a maximal string of characters delimited by spaces, tabs or newlines.
And then the actual code explicitly filters out and ignores every character larger than 0x7F. Just why.
jolmg4 months ago
Probably because they're not characters. They're just bytes undefined by ASCII.
Tor34 months ago
ASCII is 7 bits (the eight bit would be parity), so that makes perfect sense, in an ASCII world.
Joker_vD4 months ago
So the character e.g. "B" would have this parity bit set and therefore should be filtered out and not count as a letter, in the ASCII world?
aap_4 months ago
There are only 7 bits in ASCII. An 8th can be used for parity when transmitting data but a regular program will never see it. Anything above 0x7F is simply not a character.
Tor34 months ago
Parity bits are not part of the character. They are for detecting transmission errors. You filter off the parity bit before looking at the byte.
Joker_vD4 months ago
But this is not what's the code doing, is it? It's not doing (ch & 0x7F), it's doing ch <= 0x7F. And the parity checking/filtering is done in the tape drive/serial port driver anyhow, it would never reach wc in the first place.
Tor34 months ago
Yes, that's true for that code. But that wasn't really the point, the point I wrote in my earlier post was that ASCII is 7 bits, it's 0..127, and, depending on where the characters came from, only values below 128 are valid ASCII. What I was talking about was that because a parity bit was common, ASCII was limited to 7 bits, to make room for a parity bit. When other transports are involved, e.g. reading from a file, there aren't any parity bits (well, that's not entirely true - a minicomputer I worked with back in the day used parity bits on characters in text files, but that's not the case for the platform where this particular old 'wc' was used), the code simply focuses on valid ASCII, which is below 128.
epcoa4 months ago
What in the hell are you going on about? B is 0x46 which is < 0x7F.
Joker_vD4 months ago
I am going about the parity bit. 0x46 has odd number of bits set (three, to be precise) so for the parity to check out (that is, the number of bits set has to be even), a parity bit needs to be set and the resulting encoding has to be 0xC6, with four bits set.
icedchai4 months ago
Assuming parity is enabled, the parity check is done at a lower level (serial port, TTY driver, etc.) and you'll never see it from the application. I used to mess around with serial ports and terminals a ton in my youth.
Tor34 months ago
The parity bit is not part of the character. It's external, an error detecting device. To read ASCII you always look at bits 6..0, seven bits. You don't filter away the character because it has the parity bit set, you filter off the parity bit (whether it's set or not).
[deleted]4 months agocollapsed
ivan_gammel4 months ago
Because they thought that a word is something said in a human language that they can understand.
Joker_vD4 months ago
Mi ne pensas ke lingvoj kiuj usas ekskluzive la basan latinan alfabeton estas komprepeneblaj per si mem.
luismedel4 months ago
Cool how my native language is Spanish and I can almost-understand 80% of Esperanto.
actionfromafar4 months ago
Ze riform iz komplit.
Joker_vD4 months ago
The [z] and [ð] are phonemically different in English, just as [i] and [i:] are, so it'd actually be "Ðe riform is komplijt". American rhotacism prevents us from spelling it "rifoom" as would be proper, unfortunately.
dexen4 months ago
The brevity carried over to Plan 9. Re-posting my older comment (https://news.ycombinator.com/item?id=4023385):
http://en.wikipedia.org/wiki/Plan_9_from_Bell_Labs follows the Unix philosophy. A lot of legacy has been shed. I can count 13 options to ls, 11 options to sed and just 5 to sed.
The standard Plan 9 shell, Rc, is described in mere ~500 lines of manpage, while Bash takes whooping ~5400 lines.
Oh, and there is no `dll hell' in P9 :-)