feat: add string manipulation functions derived from musl libc

This commit introduces a variety of string manipulation functions, including:
- `memmem`: Searches for a substring in a memory area.
- `memmove`: Safely copies memory areas, handling overlaps.
- `mempcpy`: Copies memory and returns a pointer to the end of the destination.
- `memrchr`: Finds the last occurrence of a character in a memory area.
- `memset`: Fills a memory area with a specified value.
- `rindex`: Returns the last occurrence of a character in a string.
- `stpcpy` and `stpncpy`: Copies strings and returns a pointer to the end.
- `strcat`, `strchr`, `strcspn`, `strlcat`, `strlcpy`, `strlen`, `strncat`, `strncmp`, `strncpy`, `strnlen`, `strpbrk`, `strrchr`, `strstr`, `strtok`, and `strtok_r`: Various string manipulation functions for concatenation, searching, and tokenization.

Assembly implementations for `memcpy`, `memmove`, and `memset` are also included for optimized performance on x86_64 architectures.

1 files changed, 37 insertions, 0 deletions

diff --git a/na/lib/string/strlcpy.c b/na/lib/string/strlcpy.c
new file mode 100644
index 0000000..c2a5142
--- /dev/null
+++ b/na/lib/string/strlcpy.c
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: MIT */
+/* Derived from musl libc (Copyright © 2005-2020 Rich Felker, et al.) */
+
+#define _BSD_SOURCE
+#include <string.h>
+#include <stdint.h>
+#include <limits.h>
+
+#define ALIGN (sizeof(size_t)-1)
+#define ONES ((size_t)-1/UCHAR_MAX)
+#define HIGHS (ONES * (UCHAR_MAX/2+1))
+#define HASZERO(x) ((x)-ONES & ~(x) & HIGHS)
+
+size_t strlcpy(char *d, const char *s, size_t n)
+{
+	char *d0 = d;
+	size_t *wd;
+
+	if (!n--) goto finish;
+#ifdef __GNUC__
+	typedef size_t __attribute__((__may_alias__)) word;
+	const word *ws;
+	if (((uintptr_t)s & ALIGN) == ((uintptr_t)d & ALIGN)) {
+		for (; ((uintptr_t)s & ALIGN) && n && (*d=*s); n--, s++, d++);
+		if (n && *s) {
+			wd=(void *)d; ws=(const void *)s;
+			for (; n>=sizeof(size_t) && !HASZERO(*ws);
+			       n-=sizeof(size_t), ws++, wd++) *wd = *ws;
+			d=(void *)wd; s=(const void *)ws;
+		}
+	}
+#endif
+	for (; n && (*d=*s); n--, s++, d++);
+	*d = 0;
+finish:
+	return d-d0 + strlen(s);
+}