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, 40 insertions, 0 deletions

diff --git a/na/include/libc-shim/strings.h b/na/include/libc-shim/strings.h
new file mode 100644
index 0000000..b7a5ea0
--- /dev/null
+++ b/na/include/libc-shim/strings.h
@@ -0,0 +1,40 @@
+#ifndef	_STRINGS_H
+#define	_STRINGS_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <features.h>
+
+#define __NEED_size_t
+#define __NEED_locale_t
+#include <bits/alltypes.h>
+
+#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE) || defined(_POSIX_SOURCE) \
+ || (defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE+0 < 200809L) \
+ || (defined(_XOPEN_SOURCE) && _XOPEN_SOURCE+0 < 700)
+int bcmp (const void *, const void *, size_t);
+void bcopy (const void *, void *, size_t);
+void bzero (void *, size_t);
+char *index (const char *, int);
+char *rindex (const char *, int);
+#endif
+
+#if defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE)  || defined(_BSD_SOURCE)
+int ffs (int);
+int ffsl (long);
+int ffsll (long long);
+#endif
+
+int strcasecmp (const char *, const char *);
+int strncasecmp (const char *, const char *, size_t);
+
+int strcasecmp_l (const char *, const char *, locale_t);
+int strncasecmp_l (const char *, const char *, size_t, locale_t);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif