From f8726497a4676082bca126df7d8be48ca927abdd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=A1s=20A=2E=20Ortega?=
 <deathsbreed@themusicinnoise.net>
Date: Fri, 30 Dec 2016 17:57:28 +0100
Subject: [PATCH] Don't test for divisibility by 2.

We skip all even numbers, so we can skip 2, this also means giving 3 as
a given.
---
 src/main.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/src/main.c b/src/main.c
index 0237d87..70a6601 100644
--- a/src/main.c
+++ b/src/main.c
@@ -116,12 +116,16 @@ int main(int argc, char *argv[]) {
 			fprintf(stderr, "Failed to allocate more memory for list.\n");
 			goto releaseMemory;
 		}
-		if(!f_quiet) {
-			if(mpz_out_str(stdout, base, num) == 0)
-				fprintf(stderr, "Could not print to `stdout'!\n");
-			printf("\n");
+		// Add 3 as well to optimize the algorithm
+		mpz_set_ui(num, 3);
+		if(addToList(&primes, num) == 1) {
+			fprintf(stderr, "Failed to allocate more memory for list.\n");
+			goto releaseMemory;
 		}
-		mpz_add_ui(num, num, 1);
+		if(!f_quiet) {
+			puts("2\n3");
+		}
+		mpz_add_ui(num, num, 2);
 	} else {
 		// Load primes from file
 		int err = inputPrimes(file, &primes);
@@ -167,9 +171,10 @@ int main(int argc, char *argv[]) {
 		mpz_fdiv_q_ui(halfNum, num, 2);
 		/**
 		 * Loop through primes we've found until we get to half of the number
-		 * we're analyzing
+		 * we're analyzing. Also, skip `2' since we're not testing even
+		 * numbers.
 		 */
-		for(size_t i = 0; mpz_cmp(primes.list[i], halfNum) < 0; ++i) {
+		for(size_t i = 1; mpz_cmp(primes.list[i], halfNum) < 0; ++i) {
 			// If `num' is divisible by a prime then go to the next number
 			if(mpz_divisible_p(num, primes.list[i]) != 0)
 				goto nextNum;