Ticket #8481: 0001-strncpy-pad-the-destination-with-NULs.patch

src/system/libroot/posix/string/strncpy.c

@@ -5 +5 @@
 
 #include <sys/types.h>
 #include <string.h>
+#include <SupportDefs.h>
 
 
-char *
-strncpy(char *dest, char const *src, size_t count)
+/* From Bit twiddling hacks:
+    http://graphics.stanford.edu/~seander/bithacks.html */
+#define LACKS_ZERO_BYTE(value) \
+    (((value - 0x01010101) & ~value & 0x80808080) == 0)
+
+
+char*
+strncpy(char* dest, const char* src, size_t count)
 {
-    char *tmp = dest;
+    char* tmp = dest;
+
+    // Align destination buffer for four byte writes.
+    while (((addr_t)dest & 3) != 0 && count != 0) {
+        count--;
+        if ((*dest++ = *src++) == '\0') {
+            memset(dest, '\0', count);
+            return tmp;
+        }
+    }
+
+    if (count == 0)
+        return tmp;
+
+    if (((addr_t)src & 3) == 0) {
+        // If the source and destination are aligned, copy a word
+        // word at a time
+        uint32* alignedSrc = (uint32*)src;
+        uint32* alignedDest = (uint32*)dest;
+        size_t alignedCount = count / 4;
+        count -= alignedCount * 4;
+
+        for (; alignedCount != 0 && LACKS_ZERO_BYTE(*alignedSrc);
+                alignedCount--)
+            *alignedDest++ = *alignedSrc++;
+
+        count += alignedCount * 4;
+        src = (char*)alignedSrc;
+        dest = (char*)alignedDest;
+    }
 
-    while (count-- && (*dest++ = *src++) != '\0')
-        ;
+    // Deal with the remainder.
+    while (count-- != 0) {
+        if ((*dest++ = *src++) == '\0') {
+            memset(dest, '\0', count);
+            return tmp;
+        }
+    }
 
     return tmp;
 }