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/*
* The Great Computer Language Shootout
* http://shootout.alioth.debian.org/
*
* Written by Dima Dorfman, 2004
* Compile: gcc -std=c99 -O2 -o nsieve_bits_gcc nsieve_bits.c
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef unsigned int bits;
#define NBITS (8 * sizeof(bits))
static unsigned int
nsieve(unsigned int m)
{
unsigned int count, i, j;
bits * a;
a = malloc((m / NBITS) * sizeof(bits));
memset(a, (1 << 8) - 1, (m / NBITS) * sizeof(bits));
count = 0;
for (i = 2; i < m; ++i)
if (a[i / NBITS] & (1 << i % NBITS)) {
for (j = i + i; j < m; j += i)
a[j / NBITS] &= ~(1 << j % NBITS);
++count;
}
return (count);
}
static void
test(unsigned int n)
{
unsigned int count, m;
m = (1 << n) * 10000;
count = nsieve(m);
printf("Primes up to %8u %8u\n", m, count);
}
int
main(int ac, char **av)
{
unsigned int n;
n = ac < 2 ? 9 : atoi(av[1]);
test(n);
if (n >= 1)
test(n - 1);
if (n >= 2)
test(n - 2);
exit(0);
}
/****
build & benchmark results
BUILD COMMANDS FOR: nsievebits.gcc
Fri Sep 15 06:30:15 PDT 2006
/usr/bin/gcc -pipe -Wall -O3 -fomit-frame-pointer -funroll-loops -march=pentium4 nsievebits.c -o nsievebits.gcc_run
=================================================================
COMMAND LINE (%A is single numeric argument):
nsievebits.gcc_run %A
PROGRAM OUTPUT
==============
Primes up to 5120000 356244
Primes up to 2560000 187134
Primes up to 1280000 98610
*****/
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