As Bogdan writes, the problem is repeatedly calling `string-append`.
Instead one can make a list of all the small strings and then use
`string-join` at the end.
#lang racket
(require racket/flonum)
(define (xy->string x y)
(string-append
(~r x #:precision 1) ","
(~r y #:precision 1)))
I forgot to mention this earlier, but it might be enlightening to
run the two versions of the program with the `PLTSTDERR` environment
variable set to "error debug@GC" to see GC debug messages. For example:
env PLTSTDERR='error debug@GC' racket flvector-to-coordinates-string.rkt
>/dev/null
Hi racket-users!
I've recently become interested in Lisp/Scheme and have started to hack
in Racket. The excellent documentation, the fast integrated search, and
DrRacket have made that a real pleasure.
Thank you for that!
I've been working on a tool to convert notes from the reMarkable 2
tablet
Replacing ` (~r x #:precision 1)` with `(number->string x)` and ditto for
`y` eliminates the overhead of contracts and brings about another 4x
speedup on my machine.
That may not work, tho, depending on Alessandro's original usecase, since
the strings are different.
I was also going to, as
Hi Alessandro,
Here is a version of your program that is about 30 times faster on my
machine (9s -> 300ms):
#lang racket/base
(require racket/flonum
racket/format
racket/port)
(define (xy-vectors->string x-vec y-vec)
(call-with-output-string
On Sun, Jun 27, 2021 at 11:58 AM Alessandro Motta
wrote:
>
> I also like Jens' code for its pure functional elegance. I'm surprised
> that building up a long list of short strings before joining them is so
> much faster. After all, isn't the final `string-join` essentially doing
> what the
Den søn. 27. jun. 2021 kl. 18.58 skrev Alessandro Motta :
> I also like Jens' code for its pure functional elegance. I'm surprised
> that building up a long list of short strings before joining them is so
> much faster. After all, isn't the final `string-join` essentially doing
> what the
Anyone got an implementation of a mutable StringBuilder-like object? I
could use it in Rebellion's implementation of `into-string` which currently
isn't quadratic, but it definitely has the allocation problem.
On Sunday, June 27, 2021 at 11:36:14 AM UTC-7 bogdan wrote:
> While I think the
While I think the complexity piece is important, I feel like it's worth
pointing out just how much more expensive the allocation -- and its
ramifications, like the resulting GC pressure and CPU cache misses -- is
than one might think. Here's a quadratic version of the code that
avoids
Matthew Flatt writes:
> At Sun, 27 Jun 2021 21:36:09 +0300, Bogdan Popa wrote:
> Your program does run fast on my machine, but I think it's because this
> line doesn't have the intended bad effect:
>
>> (string-copy! dst 0 dst 0 len) ;; intentionally performing pointless
>>
Thank you all for these quick and helpful responses!
I've noticed the `call-with-output-string` mechanism while browsing
various Racket code bases, but was under the impression that this is
"just" a convenient abstraction over strings. Based on Bogdan's code and
Robby's explanation, it's now
At Sun, 27 Jun 2021 21:36:09 +0300, Bogdan Popa wrote:
> While I think the complexity piece is important, I feel like it's worth
> pointing out just how much more expensive the allocation -- and its
> ramifications, like the resulting GC pressure and CPU cache misses -- is
> than one might think.
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