خوارزميات

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uint32_t P[18];
uint32_t S[4][256];

uint32_t f (uint32_t x) {
   uint32_t h = S[0][x >> 24] + S[1][x >> 16 & 0xff];
   return ( h ^ S[2][x >> 8 & 0xff] ) + S[3][x & 0xff];
}

void blowfish_encrypt(uint32_t *L, uint32_t *R) {
    for (short r = 0; r < 16; r++) {
		*L = *L ^ P[r];
		*R = f(*L) ^ *R;
		swap(L, R);
	}
	swap(L, R);
	*R = *R ^ P[16];
	*L = *L ^ P[17];
}

void blowfish_decrypt(uint32_t *L, uint32_t *R) {
	for (short r = 17; r > 1; r--) {
		*L = *L ^ P[r];
		*R = f(*L) ^ *R;
		swap(L, R);
	}
	swap(L, R);
	*R = *R ^ P[1];
	*L = *L ^ P[0];
}

  // ...
  // initializing the P-array and S-boxes with values derived from pi; omitted in the example (you can find them below)
  // ...
  
{
	/* initialize P box w/ key*/
	uint32_t k;
	for (short i = 0, p = 0; i < 18; i++) {
		k = 0x00;
		for (short j = 0; j < 4; j++) {
			k = (k << 8) | (uint8_t) key[p];
			p = (p + 1) % key_len;
		}
		P[i] ^= k;
	}
   
	/* blowfish key expansion (521 iterations) */
	uint32_t l = 0x00, r = 0x00;
	for (short i = 0; i < 18; i+=2) {
		blowfish_encrypt(&l, &r);
		P[i] = l; 
		P[i+1] = r;
	}
	for (short i = 0; i < 4; i++) {
		for (short j = 0; j < 256; j+=2) {
			blowfish_encrypt(&l, &r);
			S[i][j] = l;
			S[i][j+1] = r;
		}
	}
}