lib: Add roundup_power_of_two()

Add a helper to round a value to the next power of two size.

And since we need fls() to implement that, reuse that elsewhere
as well.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

2 files changed, 10 insertions, 8 deletions

diff --git a/lib/igt_aux.h b/lib/igt_aux.h
index ef89faa9..192c3ad8 100644
--- a/lib/igt_aux.h
+++ b/lib/igt_aux.h
@@ -287,4 +287,10 @@ void igt_lsof(const char *dpath);
 
 #define is_power_of_two(x)  (((x) & ((x)-1)) == 0)
 
+#define igt_fls(x) ((x) ? __builtin_choose_expr(sizeof(x) == 8, \
+						64 - __builtin_clzll(x), \
+						32 - __builtin_clz(x)) : 0)
+
+#define roundup_power_of_two(x) ((x) != 0 ? 1 << igt_fls((x) - 1) : 0)
+
 #endif /* IGT_AUX_H */
diff --git a/lib/igt_fb.c b/lib/igt_fb.c
index 7c71e52a..1ba1aa7c 100644
--- a/lib/igt_fb.c
+++ b/lib/igt_fb.c
@@ -261,8 +261,6 @@ static void calc_fb_size_packed(int fd, int width, int height,
 
 	if (tiling != LOCAL_DRM_FORMAT_MOD_NONE &&
 	    intel_gen(intel_get_drm_devid(fd)) <= 3) {
-		int v;
-
 		/* Round the tiling up to the next power-of-two and the region
 		 * up to the next pot fence size so that this works on all
 		 * generations.
@@ -271,13 +269,11 @@ static void calc_fb_size_packed(int fd, int width, int height,
 		 * tiled. But then that failure is expected.
 		 */
 
-		v = byte_width;
-		for (stride = 512; stride < v; stride *= 2)
-			;
+		stride = max(byte_width, 512);
+		stride = roundup_power_of_two(stride);
 
-		v = stride * height;
-		for (size = 1024*1024; size < v; size *= 2)
-			;
+		size = max((uint64_t) stride * height, 1024*1024);
+		size = roundup_power_of_two(size);
 	} else {
 		stride = ALIGN(byte_width, tile_width);
 		size = (uint64_t) stride * ALIGN(height, tile_height);