On 11/28/2010 04:48 PM, bearophile wrote:
Pelle Månsson:
I don't have your data set,
In my first post I have explained how to create the data set, using a little
Python script that I have listed there. You just need a Python2 interpreter.
but for me using random data this was within a factor 2 of your #3, without any
fiddly code.
Thank you for your code. I have added your version, plus a modified version
that works on ubytes, because it's faster, #9 and #10:
-------------------------
// D version #9
import std.file: read;
import std.c.stdio: printf;
import std.algorithm: find;
import std.array: empty, popFront;
int test(char[] data) {
int count;
while (true) {
data = data.find("TAG", "TGA", "TAA")[0];
if (data.empty)
return count;
count++;
data.popFront();
}
}
void main() {
char[] data0 = cast(char[])read("data.txt");
int n = 300;
char[] data = new char[data0.length * n];
for (size_t pos; pos< data.length; pos += data0.length)
data[pos .. pos + data0.length] = data0;
printf("%d\n", test(data));
}
-------------------------
// D version #10
import std.file: read;
import std.c.stdio: printf;
import std.algorithm: find;
import std.array: empty, popFront;
int test(ubyte[] data) {
int count;
while (true) {
data = data.find("TAG", "TGA", "TAA")[0];
if (data.empty)
return count;
count++;
data.popFront();
}
}
void main() {
ubyte[] data0 = cast(ubyte[])read("data.txt");
int n = 300;
ubyte[] data = new ubyte[data0.length * n];
for (size_t pos; pos< data.length; pos += data0.length)
data[pos .. pos + data0.length] = data0;
printf("%d\n", test(data));
}
-------------------------
Timings, dmd compiler, best of 4, seconds:
D #1: 5.72
D #9: 5.04
D #10: 3.31
D #4: 1.84
D #5: 1.73
Psy: 1.59
D #8: 1.51
D #7: 0.56
D #2: 0.55
D #6: 0.47
D #3: 0.34
So on this PC it's not much fast. And generally I don't like to use find, empty
and popFront to solve this problem, it's quite unnatural. Here I have explained
what I think is a good enough solution to this performance problem:
http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=123044
Bye,
bearophile
Measuring incorrectly in a performance test is a silly mistake, I was
indeed wrong about the factor two thing!
I thought find was specialized for chars so it wouldn't require casting
to ubyte. Maybe I was wrong again.
Thank you for your engaging performance oriented posts. :-)
