This patch is to fix the compiler warning error: C4245. The issue will happen if the below build option is enabled: *_*_*_CC_FLAGS = -J. That's because the value of ('A' - 'a') is a negative value, which will be converted to an unsigned type if CHAR8 is treated as unsigned: Src -= ('A' - 'a'); The above issue is also recorded at: https://bugzilla.tianocore.org/show_bug.cgi?id=815. Cc: Ye Ting <ting.ye@intel.com> Cc: Fu Siyuan <siyuan.fu@intel.com> Cc: Michael Kinney <michael.d.kinney@intel.com> Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com> Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>