Improve strlen

Makefile

@@ -1,4 +1,3 @@
-CC ?= gcc
 CFLAGS := -O -g \
 	-std=c99 -pedantic
 
@@ -14,7 +13,8 @@ CFLAGS_TO_CHECK := \
 	-Wno-strict-prototypes \
 	-Wno-declaration-after-statement \
 	-Wno-format \
-	-Wno-format-pedantic
+	-Wno-format-pedantic \
+	-Wno-overflow
 
 SUPPORTED_CFLAGS :=
 # Check if a specific compiler flag is supported, attempting a dummy compilation

lib/c.c

@@ -49,10 +49,18 @@ void abort(void);
 
 int strlen(char *str)
 {
+    /* process the string by checking 4 characters (a 32-bit word) at a time */
     int i = 0;
-    while (str[i])
-        i++;
-    return i;
+    for (;; i += 4) {
+        if (!str[i])
+            return i;
+        if (!str[i + 1])
+            return i + 1;
+        if (!str[i + 2])
+            return i + 2;
+        if (!str[i + 3])
+            return i + 3;
+    }
 }
 
 int strcmp(char *s1, char *s2)