Day 5 of Advent of Code 2017
http://adventofcode.com/2017/day/5
Haskell compared with Rust
Intro
Sam H. from Reddit asked /r/haskell why his Haskell code, while not slow, was outperformed 10x faster by Rust. So I just took his Rust program and made a direct translation to Haskell.
How to run
Rust
$ cargo run -q --release
reading file into bytestring took 922 us
parsing 1058 lines took 23 us
25608482, is the answer, it took 60 ms
Haskell
$ stack build --verbosity silent && stack exec haskell
reading file into bytestring took 209.75 us
parsing 1058 lines took 47.76 us
25608482, is the answer, it took 90.28 ms
(Both programs have been ran until they repeat a lower bound.)
Haskell analysis
The Haskell code is a more or less direct translation of the Rust code. Some comments:
Using ST to deal with the vector shaves off 10ms from the answer, but this version is more direct.
You have to remember to annotate your integers, otherwise
while !(counter::Int) !(ind::Int) = dowithout the annotations is inferred as an Integer, which is about 5x
slower. GHC warns about this.
Using the mapM (\(x, line) -> ...) (zip [0..] (S.lines ...)) pattern
is less efficient than the more direct mapLinesM.
I haven't tried compiling via LLVM. I'm unable to get the backend to work on OS X. Someone else can try that.
Overall the programs run in the same order of magnitude in speed.
Haskell runtime stats
313,336 bytes allocated in the heap
64 bytes copied during GC
156,432 bytes maximum residency (1 sample(s))
81,136 bytes maximum slop
5 MB total memory in use (0 MB lost due to fragmentation)
Tot time (elapsed) Avg pause Max pause
Gen 0 0 colls, 0 par 0.000s 0.000s 0.0000s 0.0000s
Gen 1 1 colls, 0 par 0.000s 0.000s 0.0004s 0.0004s
Parallel GC work balance: nan% (serial 0%, perfect 100%)
TASKS: 18 (1 bound, 17 peak workers (17 total), using -N8)
SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)
INIT time 0.000s ( 0.002s elapsed)
MUT time 0.098s ( 0.098s elapsed)
GC time 0.000s ( 0.000s elapsed)
EXIT time 0.001s ( 0.001s elapsed)
Total time 0.132s ( 0.102s elapsed)
Alloc rate 3,206,500 bytes per MUT second
Productivity 99.5% of total user, 97.3% of total elapsed