diff options
Diffstat (limited to 'firmware/sieve.c')
-rw-r--r-- | firmware/sieve.c | 78 |
1 files changed, 78 insertions, 0 deletions
diff --git a/firmware/sieve.c b/firmware/sieve.c new file mode 100644 index 0000000..c3372f4 --- /dev/null +++ b/firmware/sieve.c @@ -0,0 +1,78 @@ +// 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); + } + } +} + |