Produce a syncmer if any minimum is at the required position

This changes the way in which ties are handled during syncmer computation,
that is, what happens when there are multiple s-mers in the k-mer that have
the same minimum hash value (most likely because the s-mers are identical).

Previously, a syncmer would be returned only if the s-mer at position t
happened to be the rightmost minimum. Now it will be returned if any of the
s-mers with minimum hash is at positon t.

This increases the number of produced syncmers.

Author: marcelm

src/randstrobes.cpp

@@ -115,7 +115,7 @@ Syncmer SyncmerIterator::next() {
                     qs_min_pos = i - s + 1;
                 }
             }
-            if (qs_min_pos == i - k + t) { // occurs at t:th position in k-mer
+            if (qs[t-1] == qs_min_val) { // occurs at t:th position in k-mer
                 uint64_t yk = std::min(xk[0], xk[1]);
                 auto syncmer = Syncmer{syncmer_kmer_hash(yk), i - k + 1};
                 i++;

tests/test_randstrobes.cpp

@@ -28,5 +28,5 @@ TEST_CASE("SyncmerIterator") {
     Syncmer syncmer;
     syncmer = si.next();
     CHECK(!syncmer.is_end());
-    CHECK(syncmer.position == 2ul);
+    CHECK(syncmer.position == 0ul);
 }