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// A simple Sieve of Eratosthenes
#include <stdint.h>
#include <stdbool.h>
#define BITMAP_SIZE 64
#define OUTPORT 0x10000000
static uint32_t bitmap[BITMAP_SIZE/32];
static void bitmap_set(int idx)
{
bitmap[idx/32] |= 1 << (idx % 32);
}
static bool bitmap_get(int idx)
{
return (bitmap[idx/32] & (1 << (idx % 32))) != 0;
}
static void print_str(const char *p)
{
while (*p != 0)
*((volatile uint32_t*)OUTPORT) = *(p++);
}
static void print_dec(int val)
{
char buffer[10];
char *p = buffer;
while (val) {
*(p++) = val % 10;
val = val / 10;
}
while (p != buffer) {
*((volatile uint32_t*)OUTPORT) = '0' + *(--p);
}
}
static void print_prime(int idx, int val)
{
if (idx < 10)
print_str(" ");
print_dec(idx);
if (idx / 10 == 1)
goto force_th;
switch (idx % 10) {
case 1: print_str("st"); break;
case 2: print_str("nd"); break;
case 3: print_str("rd"); break;
force_th:
default: print_str("th"); break;
}
print_str(" prime is ");
print_dec(val);
print_str(".\n");
}
void sieve()
{
int i, j, k;
int idx = 1;
print_prime(idx++, 2);
for (i = 0; i < BITMAP_SIZE; i++) {
if (bitmap_get(i))
continue;
print_prime(idx++, 3+2*i);
for (j = 2*(3+2*i);; j += 3+2*i) {
if (j%2 == 0)
continue;
k = (j-3)/2;
if (k >= BITMAP_SIZE)
break;
bitmap_set(k);
}
}
}
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