Add round_to_log_2()

3 files changed, 10 insertions, 2 deletions

diff --git a/src/lib/image.cc b/src/lib/image.cc
index 8e6c5717b..548c3a2b7 100644
--- a/src/lib/image.cc
+++ b/src/lib/image.cc
@@ -144,7 +144,7 @@ static
 int
 round_width_for_subsampling (int p, AVPixFmtDescriptor const * desc)
 {
-	return p & ~ ((1 << desc->log2_chroma_w) - 1);
+	return round_to_log_2 (p, desc->log2_chroma_w);
 }
 
 
@@ -152,7 +152,7 @@ static
 int
 round_height_for_subsampling (int p, AVPixFmtDescriptor const * desc)
 {
-	return p & ~ ((1 << desc->log2_chroma_h) - 1);
+	return round_to_log_2 (p, desc->log2_chroma_h);
 }
 
 
diff --git a/src/lib/util.cc b/src/lib/util.cc
index 0646a4787..33f24eeeb 100644
--- a/src/lib/util.cc
+++ b/src/lib/util.cc
@@ -1183,6 +1183,13 @@ to_upper (string s)
 }
 
 
+int
+round_to_log_2 (int x, int b)
+{
+	return x & ~ ((1 << b) - 1);
+}
+
+
 /* Set to 1 to print the IDs of some of our threads to stdout on creation */
 #define DCPOMATIC_DEBUG_THREADS 0
 
diff --git a/src/lib/util.h b/src/lib/util.h
index 013eabe12..e134804ae 100644
--- a/src/lib/util.h
+++ b/src/lib/util.h
@@ -124,6 +124,7 @@ extern dcp::DecryptedKDM decrypt_kdm_with_helpful_error (dcp::EncryptedKDM kdm);
 extern boost::filesystem::path default_font_file ();
 extern std::string to_upper (std::string s);
 extern void start_of_thread (std::string name);
+extern int round_to_log_2 (int x, int b);
 
 template <class T>
 std::list<T>