News for hackers. Stuff that matters.

A comment on Spending 3 months investigating a 7-year old bug and fixing it in 1 line of code. Parent comment

Re:Spending 3 months investigating a 7-year old bug and fixi... by drewg123 on Friday June 21, 2024 @03:16PM (#40752713)
If modulus is expensive, and he's checking a power-of-2, why not just use a bitwise AND.

Eg, for positive integers, x % 16 == x & 15. That should be trivially cheap.

[ Parent | on HN ]
Re:Spending 3 months investigating a 7-year old bug and fixi... by ladberg on Friday June 21, 2024 @03:23PM (#40752764)
It wasn't `x % 16` it was `x % y` where x and y are 16-bit integers. A compiler would also have taken care of it if it were just a literal.
[ Parent | on HN ]
Re:Spending 3 months investigating a 7-year old bug and fixi... by drewg123 on Friday June 21, 2024 @03:36PM (#40752887)
Whoops.. I misread what he was doing.
[ Parent | on HN ]
Re:Spending 3 months investigating a 7-year old bug and fixi... by xgkickt on Friday June 21, 2024 @08:43PM (#40755264)
Reading the comments, that's kinda what they did, though they had to learn that first and only now realize they only needed one.
[ Parent | on HN ]
Re:Spending 3 months investigating a 7-year old bug and fixi... by kevin_thibedeau on Friday June 21, 2024 @10:22PM (#40755668)
Any top-tier C compiler will optimize modular division by a constant into a more efficient operation(s). It is better to keep the intent of the code clear rather than devolve it into increasingly obtuse bit-twiddling tricks the compiler can figure out on its own.
[ Parent | on HN ]