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, 110 insertions, 0 deletions

diff --git a/na/include/libc-shim/string.h b/na/include/libc-shim/string.h
new file mode 100644
index 0000000..8a86304
--- /dev/null
+++ b/na/include/libc-shim/string.h
@@ -0,0 +1,110 @@
+#ifndef	_STRING_H
+#define	_STRING_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <features.h>
+
+#if __cplusplus >= 201103L
+#define NULL nullptr
+#elif defined(__cplusplus)
+#define NULL 0L
+#else
+#define NULL ((void*)0)
+#endif
+
+#define __NEED_size_t
+#if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
+ || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
+ || defined(_BSD_SOURCE)
+#define __NEED_locale_t
+#endif
+
+#include <bits/alltypes.h>
+
+void *memcpy (void *__restrict, const void *__restrict, size_t);
+void *memmove (void *, const void *, size_t);
+void *memset (void *, int, size_t);
+int memcmp (const void *, const void *, size_t);
+void *memchr (const void *, int, size_t);
+
+char *strcpy (char *__restrict, const char *__restrict);
+char *strncpy (char *__restrict, const char *__restrict, size_t);
+
+char *strcat (char *__restrict, const char *__restrict);
+char *strncat (char *__restrict, const char *__restrict, size_t);
+
+int strcmp (const char *, const char *);
+int strncmp (const char *, const char *, size_t);
+
+int strcoll (const char *, const char *);
+size_t strxfrm (char *__restrict, const char *__restrict, size_t);
+
+char *strchr (const char *, int);
+char *strrchr (const char *, int);
+
+size_t strcspn (const char *, const char *);
+size_t strspn (const char *, const char *);
+char *strpbrk (const char *, const char *);
+char *strstr (const char *, const char *);
+char *strtok (char *__restrict, const char *__restrict);
+
+size_t strlen (const char *);
+
+char *strerror (int);
+
+#if defined(_BSD_SOURCE) || defined(_GNU_SOURCE)
+#include <strings.h>
+#endif
+
+#if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
+ || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
+ || defined(_BSD_SOURCE)
+char *strtok_r (char *__restrict, const char *__restrict, char **__restrict);
+int strerror_r (int, char *, size_t);
+char *stpcpy(char *__restrict, const char *__restrict);
+char *stpncpy(char *__restrict, const char *__restrict, size_t);
+size_t strnlen (const char *, size_t);
+char *strdup (const char *);
+char *strndup (const char *, size_t);
+char *strsignal(int);
+char *strerror_l (int, locale_t);
+int strcoll_l (const char *, const char *, locale_t);
+size_t strxfrm_l (char *__restrict, const char *__restrict, size_t, locale_t);
+void *memmem(const void *, size_t, const void *, size_t);
+#endif
+
+#if defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
+ || defined(_BSD_SOURCE)
+void *memccpy (void *__restrict, const void *__restrict, int, size_t);
+#endif
+
+#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+char *strsep(char **, const char *);
+size_t strlcat (char *, const char *, size_t);
+size_t strlcpy (char *, const char *, size_t);
+void explicit_bzero (void *, size_t);
+#endif
+
+#ifdef _GNU_SOURCE
+#define	strdupa(x)	strcpy(alloca(strlen(x)+1),x)
+int strverscmp (const char *, const char *);
+char *strchrnul(const char *, int);
+char *strcasestr(const char *, const char *);
+void *memrchr(const void *, int, size_t);
+void *mempcpy(void *, const void *, size_t);
+#endif
+
+/* musl internal symbols used across translation units */
+char *__strchrnul(const char *, int);
+void *__memrchr(const void *, int, size_t);
+char *__stpcpy(char *__restrict, const char *__restrict);
+char *__stpncpy(char *__restrict, const char *__restrict, size_t);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif