-CFLAGS ?= -O2 -fomit-frame-pointer -D_BSD_SOURCE -D_GNU_SOURCE
-CFLAGS += -std=c99 -Wall -D_BSD_SOURCE -D_GNU_SOURCE
+CFLAGS ?= -O2 -fomit-frame-pointer -pipe
+CFLAGS += -std=gnu99 -D_GNU_SOURCE \
+ -Wall -Wextra -Wformat=2 -Wundef -Wno-unused-parameter \
+ -Wshadow -Wpointer-arith