5 ms·

A bit of a micro-optimization, but couldn’t you interpret 4 bytes (including the trailing null on the three-letter verbs) as a 32-bit unsigned int and then do i

A bit of a micro-optimization, but couldn’t you interpret 4 bytes (including the trailing null on the three-letter verbs) as a 32-bit unsigned int and then do integer comparisons or a case statement?

dlsa 5y ago
You could add a computed goto to really spice things up.
- stazz1 5y ago
  call it "adventure plumbing"
morelisp 5y ago
This is close to what nginx does today, if your platform supports unaligned reads. The check for 'O' is a specific fast-path only for HEAD, most others are done via ordinary comparisons.
legulere 5y ago
NGINX does exactly that (after finding the space character after the verb): https://github.com/nginx/nginx/blob/7587778a33bea0ce6f203a8c4de18e33f38b9582/src/http/ngx_http_parse.c#L38 https://github.com/nginx/nginx/blob/7587778a33bea0ce6f203a8c... There are several points to note: This trick only works if the architecture supports unaligned memory access. Macros are used instead of functions, so you don't have to rely on the compiler to do inlining. The shifts and ors should get optimized out by the compiler. I once tried something similar in C#, but sadly the JIT doesn't do that optimization.
- sseagull 5y ago
  Ah nice! I was interested in looking but don’t know the codebase. That method does look better. My idea assumes that the method has already been checked to see if it is a valid method, which has its own cost. Otherwise, POSABC would be parsed as POST. Their method does that more or less on the fly.
- MaxBarraclough 5y ago
  > This trick only works if the architecture supports unaligned memory access Presumably then it's relying on undefined behaviour.
  - stormbrew 5y ago
    pretty sure it's just implementation defined. In the sense that the implementation defines the allowed alignment, if nothing else (ie. on x86 the allowed alignment is 1 byte even if that's not optimal).
    - MaxBarraclough 5y ago
      I don't think so. What I can find on this topic with a quick search points to it being outright UB. https://stackoverflow.com/a/47622343/ https://stackoverflow.com/a/47622343/ https://stackoverflow.com/a/28895321/ https://stackoverflow.com/a/28895321/ https://blog.quarkslab.com/unaligned-accesses-in-cc-what-why-and-solutions-to-do-it-properly.html https://blog.quarkslab.com/unaligned-accesses-in-cc-what-why...

dlsa 5y ago

You could add a computed goto to really spice things up.

stazz1 5y ago
call it "adventure plumbing"

morelisp 5y ago

This is close to what nginx does today, if your platform supports unaligned reads. The check for 'O' is a specific fast-path only for HEAD, most others are done via ordinary comparisons.

legulere 5y ago

NGINX does exactly that (after finding the space character after the verb): https://github.com/nginx/nginx/blob/7587778a33bea0ce6f203a8c4de18e33f38b9582/src/http/ngx_http_parse.c#L38 https://github.com/nginx/nginx/blob/7587778a33bea0ce6f203a8c... There are several points to note: This trick only works if the architecture supports unaligned memory access. Macros are used instead of functions, so you don't have to rely on the compiler to do inlining. The shifts and ors should get optimized out by the compiler. I once tried something similar in C#, but sadly the JIT doesn't do that optimization.

sseagull 5y ago
Ah nice! I was interested in looking but don’t know the codebase. That method does look better. My idea assumes that the method has already been checked to see if it is a valid method, which has its own cost. Otherwise, POSABC would be parsed as POST. Their method does that more or less on the fly.
MaxBarraclough 5y ago
> This trick only works if the architecture supports unaligned memory access Presumably then it's relying on undefined behaviour.
- stormbrew 5y ago
  pretty sure it's just implementation defined. In the sense that the implementation defines the allowed alignment, if nothing else (ie. on x86 the allowed alignment is 1 byte even if that's not optimal).
  - MaxBarraclough 5y ago
    I don't think so. What I can find on this topic with a quick search points to it being outright UB. https://stackoverflow.com/a/47622343/ https://stackoverflow.com/a/47622343/ https://stackoverflow.com/a/28895321/ https://stackoverflow.com/a/28895321/ https://blog.quarkslab.com/unaligned-accesses-in-cc-what-why-and-solutions-to-do-it-properly.html https://blog.quarkslab.com/unaligned-accesses-in-cc-what-why...