add sys_add_three_integers

userland/include/unistd.h

@@ -157,5 +157,6 @@ char *getcwd(char *buf, size_t buflen);          /* calls __getcwd */
 time_t time(time_t *seconds);                    /* calls __time */
 
 int printchar(char c);
+int add_three_integers(int a, int b, int c);
 
 #endif /* _UNISTD_H_ */

userland/testbin/Makefile

@@ -5,7 +5,7 @@
 TOP=../..
 .include "$(TOP)/mk/os161.config.mk"
 
-SUBDIRS=add argtest badcall bigexec bigfile bigfork bigseek bloat conman \
+SUBDIRS=add add_three_integers argtest badcall bigexec bigfile bigfork bigseek bloat conman \
 	crash ctest dirconc dirseek dirtest f_test factorial farm faulter \
 	filetest forkbomb forktest frack hash hog huge \
 	malloctest matmult multiexec palin parallelvm poisondisk printchartest psort \

userland/testbin/add_three_integers/Makefile

@@ -0,0 +1,10 @@
+# Makefile for add_three_integers
+
+TOP=../../..
+.include "$(TOP)/mk/os161.config.mk"
+
+PROG=add_three_integers
+SRCS=add_three_integers.c
+BINDIR=/testbin
+
+.include "$(TOP)/mk/os161.prog.mk"

userland/testbin/add_three_integers/add_three_integers.c

@@ -0,0 +1,10 @@
+#include <unistd.h>
+
+extern int add_three_integers(int a, int b, int c);
+
+int main() {
+  add_three_integers(3, 5, 2);  // should output 10
+  add_three_integers(-5, 3, 1); // should output -1
+
+  return 0;
+}