Two minor improvements from libvpx

1. mem.h: improve the macro to handle n==0
2. borders_test.cc: fix a typo in

Change-Id: I24729aaf7282b2080d9a8325d481887b54341260

aom_ports/mem.h

@@ -38,8 +38,8 @@
 #define __builtin_prefetch(x)
 #endif
 
-/* Shift down with rounding */
-#define ROUND_POWER_OF_TWO(value, n) (((value) + (1 << ((n)-1))) >> (n))
+/* Shift down with rounding for use when n >= 0, value >= 0 */
+#define ROUND_POWER_OF_TWO(value, n) (((value) + (((1 << (n)) >> 1))) >> (n))
 
 /* Shift down with rounding for signed integers, for use when n >= 0 */
 #define ROUND_POWER_OF_TWO_SIGNED(value, n)           \

test/borders_test.cc

@@ -55,7 +55,7 @@ TEST_P(BordersTest, TestEncodeHighBitrate) {
   // extend into the border and test the border condition.
   cfg_.g_lag_in_frames = 25;
   cfg_.rc_2pass_vbr_minsection_pct = 5;
-  cfg_.rc_2pass_vbr_minsection_pct = 2000;
+  cfg_.rc_2pass_vbr_maxsection_pct = 2000;
   cfg_.rc_target_bitrate = 2000;
   cfg_.rc_max_quantizer = 10;