From b26818e31c9588290d42c62628cef6a6d07442ac Mon Sep 17 00:00:00 2001
From: Ulrich Bauer <ulrich.bauer@tum.de>
Date: Tue, 10 May 2016 22:23:04 +0200
Subject: primality check

---
 ripser.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/ripser.cpp b/ripser.cpp
index 8a44b50..e04723d 100644
--- a/ripser.cpp
+++ b/ripser.cpp
@@ -776,8 +776,9 @@ void compute_pairs(
     #endif
 }
 
-bool is_prime(const unsigned long n) {
-    for (unsigned long i = 2; i*i <= n; ++i) if (n%i == 0) return false;
+bool is_prime(const coefficient_t n) {
+    if (!(n & 1) || n < 2 ) return n == 2;
+    for (coefficient_t p = 3, q = n/p, r = n%p; p <= q; p += 2, q = n/p, r = n%p) if (!r) return false;
     return true;
 }
 
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