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// The Computer Language Shootout
// http://shootout.alioth.debian.org/
// Precedent C entry modified by bearophile for speed and size, 31 Jan 2006
// Compile with: -O3 -s -std=c99 -fomit-frame-pointer
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef unsigned char boolean;
static void nsieve(int m) {
unsigned int count = 0, i, j;
boolean * flags = (boolean *) malloc(m * sizeof(boolean));
memset(flags, 1, m);
for (i = 2; i < m; ++i)
if (flags[i]) {
++count;
for (j = i << 1; j < m; j += i)
if (flags[j]) flags[j] = 0;
}
free(flags);
printf("Primes up to %8u %8u\n", m, count);
}
int main(int argc, char * argv[]) {
int m = argc < 2 ? 9 : atoi(argv[1]);
int i;
for (i = 0; i < 3; i++)
nsieve(10000 << (m-i));
return 0;
}
/********
build & benchmark results
BUILD COMMANDS FOR: nsieve.gcc
Thu Sep 14 20:51:46 PDT 2006
/usr/bin/gcc -pipe -Wall -O3 -fomit-frame-pointer -funroll-loops -march=pentium4 -s -std=c99 nsieve.c -o nsieve.gcc_run
=================================================================
COMMAND LINE (%A is single numeric argument):
nsieve.gcc_run %A
N=9
PROGRAM OUTPUT
==============
Primes up to 5120000 356244
Primes up to 2560000 187134
Primes up to 1280000 98610
*******/
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