Re: Searching strings with indexOf vs countUntil
On Thursday, 25 May 2017 at 18:13:15 UTC, Anonymouse wrote:
Part of the strings I'm working with can be assumed to be only
ASCII, yes. indexOf only wants strings or char[]s, but
interestingly if I use the same benchmark but have countUntil
work on raw ubyte[]s, it is faster. See
https://dpaste.dzfl.pl/2e095f7d18be.
There's a less ugly cast in std.string:
import std.string : representation;
//(cast(ubyte[])line).countUntil(cast(ubyte[])" :");
line.representation.countUntil(" :".representation);
Re: Searching strings with indexOf vs countUntil
On Thursday, 25 May 2017 at 11:55:21 UTC, Kagamin wrote:
I would guess indexOf returns a value suitable for indexing,
therefore it counts code units, while countUntil counts range
elements - code points in case of a string. Also number of code
points is not suitable for indexing an utf8 string, it can be
used to allocate a dstring, but not so much for anything else.
What do you use the resulting value for?
I see. I would have thought indexOf would be more keen to decode,
but that's bias talking.
The project is an IRC bot. I use indexOf/used countUntil to slice
up strings into one part leading up to some separator (" :" in
that example), and another into everything after it. See
https://dpaste.dzfl.pl/326e450058c1.
On Thursday, 25 May 2017 at 12:46:43 UTC, Basile B. wrote:
To get rid of decoding he can cast to ubyte[]. I would do that
if sure that the input is only made of ascii chars.
Part of the strings I'm working with can be assumed to be only
ASCII, yes. indexOf only wants strings or char[]s, but
interestingly if I use the same benchmark but have countUntil
work on raw ubyte[]s, it is faster. See
https://dpaste.dzfl.pl/2e095f7d18be.
Re: Searching strings with indexOf vs countUntil
On Thursday, 25 May 2017 at 11:55:21 UTC, Kagamin wrote: I would guess indexOf returns a value suitable for indexing, therefore it counts code units, while countUntil counts range elements - code points in case of a string. Also number of code points is not suitable for indexing an utf8 string, it can be used to allocate a dstring, but not so much for anything else. What do you use the resulting value for? To get rid of decoding he can cast to ubyte[]. I would do that if sure that the input is only made of ascii chars.
Re: Searching strings with indexOf vs countUntil
I would guess indexOf returns a value suitable for indexing, therefore it counts code units, while countUntil counts range elements - code points in case of a string. Also number of code points is not suitable for indexing an utf8 string, it can be used to allocate a dstring, but not so much for anything else. What do you use the resulting value for?
Searching strings with indexOf vs countUntil
I was profiling my program with callgrind and saw that a lot of
time was spent in countUntil (std.algorithm.searching) on
strings. I had chosen to use it instead of indexOf (std.string),
with the plain assumption that countUntil wouldn't decode, while
indexOf would.
Comparing microbenchmarks between the two I see that countUntil
is some 7x slower.
import std.stdio : writeln;
import std.string : indexOf;
import std.algorithm.searching : countUntil;
import std.datetime;
enum line = ":zorael!~n...@asdf.asdf.asdf PRIVMSG #d :Hello
world!";
enum iterations = 1_000_000;
void main()
{
StopWatch sw;
sw.start();
foreach (i; 0..iterations)
{
line.indexOf(" :");
}
sw.stop();
immutable usecsIndexOf = sw.peek().usecs;
sw.reset();
sw.start();
foreach (i; 0..iterations)
{
line.countUntil(" :");
}
sw.stop();
immutable usecsCountUntil = sw.peek().usecs;
writeln("indexOf:", usecsIndexOf.usecs);
writeln("countUntil: ", usecsCountUntil.usecs);
writeln(cast(double)usecsCountUntil/usecsIndexOf, "x");
}
https://dpaste.dzfl.pl/0319edb79ec8 gives the output:
indexOf:160 ms and 534 μs
countUntil: 1 sec, 146 ms, and 842 μs
7.14392x
What is the fundamental difference between the two? When should I
ever use countUntil on strings?
