Sieve of Eratosthenes

This is an eaxmple of the Sieve of Eratosthenes.

#define MAX_NUMBER (2904)
#define MAX_SIZE ((MAX_NUMBER+15) / 16)

int sieve[MAX_SIZE];
/*
int masks[8] = {1, 2, 4, 8, 16, 32, 64, 128};
int invMasks[8] = {0xfe, 0xfd, 0xfb, 0xf7, 0xef, 0xdf, 0xbf, 0x7f};
*/
int masks[8] = {128, 64, 32, 16, 8, 4, 2, 1};
int invMasks[8] = {0x7f, 0xbf, 0xdf, 0xef, 0xf7, 0xfb, 0xfd, 0xfe};

int prime(int i)
 { /* BEGIN FUNCTON prime */
    int i1;
    int idx;
    int bit;
    int toReturn;

    /* is it even */
    if (0 == (1 & i))
        toReturn = (1 == 0);
     else
      { /* now check the odd numbers */
    /* figure out which bit belongs to current number */
    /* shift right 1 to divide by 2 because we skip even numbers */
    /* subtract 1 because we use 0-based indexing */
        i1 = (i >> 1) - 1;
        idx = i1 >> 3;
        bit = i1 & 7;
        toReturn = (0 != (sieve[idx] & masks[bit]));
      } /* now check the odd numbers */
     return toReturn;
 } /* END FUNCTON prime */

void initSieve()
 { /* BEGIN FUNCTON initSieve */
    int i;
    int i1;
    int n;
    int t;
    int idx;

    /* turn on all bits */
    for (i=0; i < MAX_SIZE; i++) sieve[i] = 0xffff;
    
    /* loop for each odd number */
    for (i=3; MAX_NUMBER>i; i=i+2)
     { /* loop for each possibe prime */
        if (prime(i))
         { /* number is prime */
printf("%d\n", i);
            n = (i >> 1) - 1;
            idx = n >> 3;
            while (MAX_SIZE > idx)
             { /* while more numbers */
                n = (n & 7) + i;
                t = n >> 3;
                if (0 < t)
                 { /* move to another word */
                    idx = idx + t;
                    n = n & 7;
                 } /* move to another word */
                sieve[idx] = sieve[idx] & invMasks[n];
               //  printf("i=%d  test=%d idx=%d   n=%d   sieve=%x\n", i, (((idx*8)+n)*2)+3, idx, n, sieve[idx]);
             } /* while more numbers */
         } /* number is prime */
     } /* loop for each possibe prime */
 } /* END FUNCTON initSieve */