Added `_str_raw_to_cstrsa()`: Convert raw buffer to nul-terminated string that is dynamically allocated and statically held. (i.e. do not `free()`)

Fortune for naka's current commit: Blessing − 吉

src/str.c

@@ -31,7 +31,50 @@ struct string {
 
 //TODO: We can use offsetof() to reverse the result of `str_new()` from char* (str field) to str_t*.
 
+inline static isize _str_wrap_index(usize _max, isize wr)
+{
+	isize max = (isize)_max;
+	ifU(max<0) FATAL("max too large, must be <= isize::max (%lu)", SIZE_MAX>>1);
+	else if(!max) return 0;
+
+	while(wr<0) wr = max + wr;
+	wr = wr >=max ? wr % max : wr;
+	debug_assert(wr>0);
+	return wr;
+}
+
+// Create a cstring (nul-terminated) from `from`. This string is statically allocated and should not be modified.
+// `sl` - Max size of `from` buffer. If 0, then just free the allocated buffer and return empty string;
+// `from` - Non-nul-terminated string buffer to copy from. 
+// `len` - A pointer to a wrappable index for `from`. If `len` is negative, then offset from `sl`, if it's positive, offset from 0; if it's NULL, use `sl` itself. It is wrapped around `sl` in the case that the computed offset is >= sl.
+//
+// # Notes
+// Don't `free()` this returned pointer, this function handles that on call and on program exit.
+static const char* _str_raw_to_cstrsa(usize sl, const char from[restrict sl], isize*pINOUT len)
+{
+	static _Thread_local char* _ma_buf = NULL;
+
+	if(!sl) {
+		free(_ma_buf); //free(NULL) is allowed.
+		_ma_buf=NULL;
+		return "";
+	}
 
+	_callcv(exit) void _cleanup() { free(_ma_buf); _ma_buf = NULL; }
+
+	isize fp = (isize) (sl & (SIZE_MAX >> 1));
+	if(!len) len = &fp;
+	TRACE("copying wrapped %ld bytes from buffer %p[%lu]", *len, from, sl);
+	
+	
+	usize rl = (usize) (*len = _str_wrap_index(sl, *len));
+	
+	if(_ma_buf)	_ma_buf = realloc(_ma_buf, rl+1);
+	else		_ma_buf = malloc(rl+1);
+	memmove(_ma_buf, from, rl);
+	_ma_buf[rl] = 0;
+	return (const char*)_ma_buf;
+}
 
 inline static bool _str_meta_is_owned(enum str_ownership owned)
 {