107 lines
1.9 KiB
C
107 lines
1.9 KiB
C
// Taken from picorv32
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//
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// This is free and unencumbered software released into the public domain.
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//
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// Anyone is free to copy, modify, publish, use, compile, sell, or
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// distribute this software, either in source code form or as a compiled
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// binary, for any purpose, commercial or non-commercial, and by any
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// means.
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// A simple Sieve of Eratosthenes
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#include <stdio.h>
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#include <stdint.h>
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/*************************************************************************/
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// Note: if this is changed, then checksum need
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// to be updated as well.
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#define BITMAP_SIZE 64
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typedef int bool;
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static uint32_t bitmap[BITMAP_SIZE/32];
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static uint32_t hash;
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static uint32_t mkhash(uint32_t a, uint32_t b)
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{
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// The XOR version of DJB2
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return ((a << 5) + a) ^ b;
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}
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static void bitmap_set(int idx)
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{
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bitmap[idx/32] |= 1 << (idx % 32);
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}
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static bool bitmap_get(int idx)
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{
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return (bitmap[idx/32] & (1 << (idx % 32))) != 0;
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}
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static void print_prime(int idx, int val)
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{
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if (idx < 10)
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printf(" ");
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printf("%d",idx);
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if (idx / 10 == 1)
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goto force_th;
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switch (idx % 10) {
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case 1: printf("st"); break;
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case 2: printf("nd"); break;
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case 3: printf("rd"); break;
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force_th:
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default: printf("th"); break;
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}
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printf(" prime: %d\n",val);
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hash = mkhash(hash, idx);
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hash = mkhash(hash, val);
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}
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void sieve(void)
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{
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int idx = 1;
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hash = 5381;
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print_prime(idx++, 2);
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for (int i = 0; i < BITMAP_SIZE; i++) {
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if (bitmap_get(i))
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continue;
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print_prime(idx++, 3+2*i);
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for (int j = 2*(3+2*i);; j += 3+2*i) {
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if (j%2 == 0)
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continue;
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int k = (j-3)/2;
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if (k >= BITMAP_SIZE)
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break;
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bitmap_set(k);
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}
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}
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printf("checksum:\n %x",hash);
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if (hash == 0x1772A48F) {
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printf(" OK\n");
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} else {
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printf(" ERROR\n");
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}
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}
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int main(void)
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{
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for(;;) {
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sieve();
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for(int i=0; i<10; ++i) {
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wait();
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}
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}
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return 0;
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}
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