include/intarith: introduce round_down_to()

Same as with round_up_to(), d isn't required to be a power of two.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
(cherry picked from commit 94bf3a5d74cfd61e0bd881ca2863fe2205f27767)

Conflicts:
	src/librbd/api/DiffIterate.cc [ commit 6eb14774fec0 ("librbd:
	  build without "using namespace std"") not in pacific ]

diff --git a/src/include/intarith.h b/src/include/intarith.h
index e912cbe7b3c44f242921f298dcd8dd0b4dc11e16..a4ac36d4934e8a5710b7f8cea050ad29d5994e5e 100644 (file)
--- a/src/include/intarith.h
+++ b/src/include/intarith.h
@@ -22,6 +22,10 @@ constexpr inline std::make_unsigned_t<std::common_type_t<T, U>> div_round_up(T n
   return (n + d - 1) / d;
 }
 
+template<typename T, typename U>
+constexpr inline std::make_unsigned_t<std::common_type_t<T, U>> round_down_to(T n, U d) {
+  return n - n % d;
+}
 
 template<typename T, typename U>
 constexpr inline std::make_unsigned_t<std::common_type_t<T, U>> round_up_to(T n, U d) {

diff --git a/src/librbd/api/DiffIterate.cc b/src/librbd/api/DiffIterate.cc
index 6ded254f0992c662948dee5494d67e8b4dce0a5c..edc1811256e7ff2c474bef34b9edeeffc7551084 100644 (file)
--- a/src/librbd/api/DiffIterate.cc
+++ b/src/librbd/api/DiffIterate.cc
@@ -291,7 +291,7 @@ int DiffIterate<I>::execute() {
   uint64_t left = m_length;
 
   while (left > 0) {
-    uint64_t period_off = off - (off % period);
+    uint64_t period_off = round_down_to(off, period);
     uint64_t read_len = min(period_off + period - off, left);
 
     if (fast_diff_enabled) {