usr: Add a strcmp example

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

2 files changed, 38 insertions, 0 deletions

diff --git a/arch/riscv/usr/basics.c b/arch/riscv/usr/basics.c
index 9b2267e..1d822c3 100644
--- a/arch/riscv/usr/basics.c
+++ b/arch/riscv/usr/basics.c
@@ -132,6 +132,25 @@ void test_atomic_add(void)
 	printf("atomic_add:\t\tOK\n");
 }
 
+extern int mstrcmp(const char *s1, const char *s2);
+
+void test_mstrcmp(void)
+{
+	char *strings[] = {
+		"hello", "", "iello", "helloa", "contammusaaquellhomedegranarditquetantissimerra",
+	};
+
+	for (uint64_t i = 0; i < 1000000000; i++) {
+		assert(mstrcmp(strings[0], strings[0]) == 0);
+		assert(mstrcmp(strings[0], strings[1]) > 0);
+		assert(mstrcmp(strings[0], strings[2]) < 0);
+		assert(mstrcmp(strings[0], strings[3]) < 0);
+		assert(mstrcmp(strings[0], strings[4]) > 0);
+	}
+
+	printf("mstrcmp:\t\tOK\n");
+}
+
 int main()
 {
 	test_factorial();
@@ -139,4 +158,5 @@ int main()
 	test_is_palindrome();
 	test_greater_than_ten();
 	test_atomic_add();
+	test_mstrcmp();
 }
diff --git a/arch/riscv/usr/string.S b/arch/riscv/usr/string.S
index 0f3bcc1..3878074 100644
--- a/arch/riscv/usr/string.S
+++ b/arch/riscv/usr/string.S
@@ -91,3 +91,21 @@ palindrome_yes:
 palindrome_no:
     li a0, 0
     jr ra
+
+.globl mstrcmp
+.type mstrcmp, @function
+
+// int mstrcmp(const char *, const char *);
+mstrcmp:
+1:
+	lbu t0, 0(a0)
+	lbu t1, 0(a1)
+	bne t0, t1, 2f
+	addi a0, a0, 1
+	addi a1, a1, 1
+	bnez t0, 1b
+	li a0, 0
+	ret
+2:
+	sub a0, t0, t1
+	ret