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 | Posted by bearophile_hugs@eml.cc |  Permalink Reply |
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bearophile_hugs@eml.cc 
| http://d.puremagic.com/issues/show_bug.cgi?id=6271
Summary: std.string.join performance
Product: D
Version: D2
Platform: x86
OS/Version: Windows
Status: NEW
Severity: enhancement
Priority: P2
Component: Phobos
AssignedTo: nobody@puremagic.com
ReportedBy: bearophile_hugs@eml.cc
--- Comment #0 from bearophile_hugs@eml.cc 2011-07-08 17:37:11 PDT ---
I think join() is used often on short strings (arrays of chars). A benchmark:
alias char[][] Mat;
string joinSlow(Mat table) {
import std.string;
return cast(string)join(table);
}
string joinFast(Mat table) {
size_t totLen = 0;
foreach (row; table)
totLen += row.length;
auto result = new char[totLen];
int pos = 0;
foreach (row; table)
foreach (ch; row)
result[pos++] = ch;
return cast(string)result;
}
void main() {
import std.stdio;
import std.datetime;
char[][] data = ["abcdefg".dup, "abcdefg".dup,
"abcdefg".dup, "ABCDEFG".dup,
"XXXXXXX".dup, "abcdefg".dup,
"abcdefgh".dup, "1234567".dup];
enum size_t N = 500_000;
writeln("N = ", N);
StopWatch sw;
if (joinSlow(data) != joinFast(data))
throw new Exception("Not the same results");
foreach (_; 0 .. 2) {
sw.start();
foreach (i; 0U .. N)
joinSlow(data);
sw.stop();
writeln("joinSlow: ", sw.peek().msecs);
sw.reset();
sw.start();
foreach (i; 0U .. N)
joinFast(data);
sw.stop();
writeln("joinFast: ", sw.peek().msecs);
sw.reset();
}
}
Output on my PC (DMD 2.054beta):
N = 500000
joinSlow: 2088
joinFast: 200
joinSlow: 2060
joinFast: 199
(This has caused some performance loss in my code.)
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