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, 21 insertions, 0 deletions

diff --git a/na/include/libc-shim/stdint.h b/na/include/libc-shim/stdint.h
new file mode 100644
index 0000000..650bdcf
--- /dev/null
+++ b/na/include/libc-shim/stdint.h
@@ -0,0 +1,21 @@
+/* Shim: stdint types for musl string functions */
+#ifndef _STDINT_H
+#define _STDINT_H
+
+typedef unsigned char      uint8_t;
+typedef unsigned short     uint16_t;
+typedef unsigned int       uint32_t;
+typedef unsigned long      uint64_t;
+typedef signed char        int8_t;
+typedef signed short       int16_t;
+typedef signed int         int32_t;
+typedef signed long        int64_t;
+typedef unsigned long      uintptr_t;
+typedef long               intptr_t;
+
+#define UINT8_MAX  0xFF
+#define UINT16_MAX 0xFFFF
+#define UINT32_MAX 0xFFFFFFFFU
+#define UINT64_MAX 0xFFFFFFFFFFFFFFFFUL
+
+#endif