kern/string: implement strncmp

2 files changed, 24 insertions, 0 deletions

diff --git a/kern/string.c b/kern/string.c
index b77aa2f3..584030b9 100644
--- a/kern/string.c
+++ b/kern/string.c
@@ -177,6 +177,29 @@ strcmp(const char *s1, const char *s2)
 }
 #endif /* ARCH_STRING_STRCMP */
 
+#ifndef ARCH_STRING_STRNCMP
+int
+strncmp(const char *s1, const char *s2, size_t n)
+{
+    char c1, c2;
+
+    c1 = '\0';
+    c2 = '\0';
+
+    while ((n != 0) && (c1 = *s1) == (c2 = *s2)) {
+        if (c1 == '\0') {
+            return 0;
+        }
+
+        n--;
+        s1++;
+        s2++;
+    }
+
+    return (int)c1 - (int)c2;
+}
+#endif /* ARCH_STRING_STRNCMP */
+
 #ifndef ARCH_STRING_STRCHR
 char *
 strchr(const char *s, int c)
diff --git a/kern/string.h b/kern/string.h
index 86786c2b..35490ffa 100644
--- a/kern/string.h
+++ b/kern/string.h
@@ -28,6 +28,7 @@ size_t strlen(const char *s);
 char * strcpy(char *dest, const char *src);
 size_t strlcpy(char *dest, const char *src, size_t n);
 int strcmp(const char *s1, const char *s2);
+int strncmp(const char *s1, const char *s2, size_t n);
 char * strchr(const char *s, int c);
 
 #endif /* _KERN_STRING_H */