From 703121f8671d8d131cf6a6b72e23d63688590c26 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Sat, 23 Sep 2017 00:13:16 -0700
Subject: [PATCH] ircd::db: Add reverse string_view comparator.

---
 include/ircd/db/comparator.h | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/ircd/db/comparator.h b/include/ircd/db/comparator.h
index f72194eec..9db3efb95 100644
--- a/include/ircd/db/comparator.h
+++ b/include/ircd/db/comparator.h
@@ -29,6 +29,7 @@ namespace ircd::db
 
 	struct cmp_int64_t;
 	struct cmp_string_view;
+	struct reverse_cmp_string_view;
 }
 
 struct ircd::db::comparator
@@ -38,6 +39,24 @@ struct ircd::db::comparator
 	std::function<bool (const string_view &, const string_view &)> equal;
 };
 
+struct ircd::db::reverse_cmp_string_view
+:db::comparator
+{
+	static bool less(const string_view &a, const string_view &b)
+	{
+		return std::memcmp(a.data(), b.data(), std::min(a.size(), b.size())) > 0;
+	}
+
+	static bool equal(const string_view &a, const string_view &b)
+	{
+		return a == b;
+	}
+
+	reverse_cmp_string_view()
+	:db::comparator{"reverse_string_view", &less, &equal}
+	{}
+};
+
 struct ircd::db::cmp_string_view
 :db::comparator
 {
@@ -52,7 +71,7 @@ struct ircd::db::cmp_string_view
 	}
 
 	cmp_string_view()
-	:db::comparator{"string_view", less, equal}
+	:db::comparator{"string_view", &less, &equal}
 	{}
 };
 
@@ -78,6 +97,6 @@ struct ircd::db::cmp_int64_t
 	}
 
 	cmp_int64_t()
-	:db::comparator{"int64_t", less, equal}
+	:db::comparator{"int64_t", &less, &equal}
 	{}
 };