Optimization (ITS8020) - Redigeerimiste ajalugu

Irve: /* Hints */

2018-11-30T09:37:17Z

Hints

Irve: /* Programm */

2018-11-30T09:36:54Z

Programm

Irve – 30. november 2018, kell 09:36

2018-11-30T09:36:22Z

Irve: Uus lehekülg: '''Optimization of a program'' (Also available in [http://lambda.ee/w/index.php?title=Optimization_(ITI8510)&oldid=12060 Estonian]) == Programm == Write a program which will rea...'

2018-11-30T09:36:12Z

Uus lehekülg: '''Optimization of a program'' (Also available in [http://lambda.ee/w/index.php?title=Optimization_(ITI8510)&oldid=12060 Estonian]) == Programm == Write a program which will rea...'

Uus lehekülg

''Optimization of a program'' (Also available in [http://lambda.ee/w/index.php?title=Optimization_(ITI8510)&oldid=12060 Estonian])

== Programm ==

Write a program which will read a file and outputs its statistics.

* For a "standard" input file with random content, please run:
dd if=/dev/urandom of=random_file count=1048576 bs=1

* The output of the program should be 256 human-readable lines of ASCII numbers, which represent the content of the file. The first line should contain the number of occurences of byte with a value of 0x0 (or binary zero) in the file and the last line the number of occurences of byte with value 0xff (or 256 in decimal).
* Measure the running time of the program with:
time programname

== Hints ==

* Does the loop unrolling trick work?
* Perhaps it is possible to use parallel programming or threads?
* Does compilation optimization with -O work?
* Can you replace printf with something faster that you write yourself?
* Perhaps the keyword inline can be used.
* (Sadly mmap for file reading fails in dijkstra) Can you speed up the reading of the file with mmap()? (Note -- mmap not yet explained in the lecture)

== Example code for base program ==

#include <stdlib.h>
#include <stdio.h>

long int stats[256];

int main() {
int i, c;
FILE * f;

f = fopen("random_file", "r");
if(f == NULL) {
perror("slowstat");
exit(EXIT_FAILURE);
}

while((c = fgetc(f)) != EOF) {
stats[c]++;
}

for(i = 0; i < 255; i++) {
printf("%ld\n", stats[i]);
}
exit(EXIT_SUCCESS);
}

←Vanem redaktsioon		Redaktsioon: 30. november 2018, kell 09:36
1. rida:		1. rida:
−	''Optimization of a program'' ~~(Also available in [http://lambda.ee/w/index.php?title=Optimization_(ITI8510)&oldid=12060 Estonian])~~	+	''Optimization of a program''
−
	== Programm ==		== Programm ==

@@ 18. rida: / 18. rida: @@
 * Can you replace printf with something faster that you write yourself?
 * Perhaps the keyword inline can be used.
-* (Sadly mmap for file reading fails in dijkstra) Can you speed up the reading of the file with mmap()? (Note -- mmap not yet explained in the lecture)
+* (Sadly mmap for file reading fails in dijkstra) Can you speed up the reading of the file with mmap()?
 == Example code for base program ==

@@ 7. rida: / 7. rida: @@
   dd if=/dev/urandom of=random_file count=1048576 bs=1
-* The output of the program should be 256 human-readable lines of ASCII numbers, which represent the content of the file. The first line should contain the number of occurences of byte with a value of 0x0 (or binary zero) in the file and the last line the number of occurences of byte with value 0xff (or 256 in decimal).
+* The output of the program should be 256 human-readable lines of ASCII numbers, which represent the content of the file. The first line should contain the number of occurences of byte with a value of 0x0 (or binary zero) in the file and the last line the number of occurences of byte with value 0xff (or 255 in decimal).
 * Measure the running time of the program with:
   time programname