string: add creationg and char access functions

include/neo/_string.h

@@ -0,0 +1,52 @@
+/** See the end of this file for copyright and license terms. */
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "neo/_types.h"
+
+/**
+ * Copy a regular C string to a neo string.
+ *
+ * `s` must be NUL terminated, and be deallocated manually if no longer needed.
+ * If `s` is `nil` or allocation fails, an error is yeeted.  Strings in libneo
+ * are reference counted, see `nget` and `nput`.
+ *
+ * @param s: String to convert
+ * @param err: Error pointer
+ * @returns The converted string, unless an error occurred
+ */
+string *nstr(const char *restrict s, error *err);
+
+/**
+ * Get the Unicode code point in a string at the specified index.
+ *
+ * If the string is `nil` or the index is out of range, an error is yeeted.
+ *
+ * @param s: String to get a character from
+ * @param index: Character index, starting from 0
+ * @param err: Error pointer
+ * @returns The Unicode code point at the specified index,
+ *	unless an error occurred
+ */
+nchar nchrat(string *s, usize index, error *err);
+
+#ifdef __cplusplus
+}; /* extern "C" */
+#endif
+
+/*
+ * This file is part of libneo.
+ * Copyright (c) 2021 Fefie <owo@fef.moe>.
+ *
+ * libneo is non-violent software: you may only use, redistribute,
+ * and/or modify it under the terms of the CNPLv6+ as found in
+ * the LICENSE file in the source code root directory or at
+ * <https://git.pixie.town/thufie/CNPL>.
+ *
+ * libneo comes with ABSOLUTELY NO WARRANTY, to the extent
+ * permitted by applicable law.  See the CNPLv6+ for details.
+ */

src/string/nstr.c

@@ -0,0 +1,99 @@
+/** See the end of this file for copyright and license terms. */
+
+#include <errno.h>
+#include <string.h>
+
+#include "neo/_error.h"
+#include "neo/_nalloc.h"
+#include "neo/_nref.h"
+#include "neo/_string.h"
+#include "neo/_types.h"
+#include "neo/utf.h"
+
+static void nstr_destroy(string *str)
+{
+	nfree(str->_data);
+	nfree(str);
+}
+
+string *nstr(const char *restrict s, error *err)
+{
+	if (s == nil) {
+		yeet(err, EFAULT, "String must not be nil");
+		return nil;
+	}
+
+	string *str = nalloc(sizeof(*str), err);
+	catch(err) {
+		return nil;
+	}
+
+	/*
+	 * neo strings are terminated by four NUL characters rather than just
+	 * one.  We do this to make sure nothing bad can happen if some stupid
+	 * UTF-8 implementation (read: my UTF-8 implementation) reads beyond the
+	 * last byte if it is malformed to suggest the beginning of a multibyte
+	 * sequence when it is actually not.  The rationale behind this is that
+	 * it is way easier to write a branchless decoder if it is allowed to
+	 * always read up to four bytes rather than honor an unexpected NUL
+	 * terminator within a multibyte sequence.
+	 *
+	 * Yeah, this is definitely never gonna break my legs.
+	 */
+	usize nbytes = strlen(s) + 4;
+	str->_data = nalloc(nbytes, err);
+	catch(err) {
+		nfree(str);
+		return nil;
+	}
+
+	strcpy(str->_data, s);
+	str->_data[nbytes - 3] = '\0';
+	str->_data[nbytes - 2] = '\0';
+	str->_data[nbytes - 1] = '\0';
+	str->_len = utf8_strlen(str->_data);
+	str->_capacity = nbytes;
+	nref_init(str, nstr_destroy);
+
+	return str;
+}
+
+nchar nchrat(string *s, usize index, error *err)
+{
+	if (s == nil) {
+		yeet(err, EFAULT, "String is nil");
+		return '\0';
+	}
+
+	nget(s);
+
+	if (index >= s->_len) {
+		yeet(err, ERANGE, "String index out of bounds");
+		return '\0';
+	}
+
+	char *ptr = s->_data;
+	while (index != 0)
+		index -= (*ptr++ & 0xc0) != 0x80;
+	ptr--;
+
+	nchar ret;
+	utf8_to_nchr(&ret, ptr, err);
+
+	nput(s);
+
+	return ret;
+}
+
+/*
+ * This file is part of libneo.
+ * Copyright (c) 2021 Fefie <owo@fef.moe>.
+ *
+ * libneo is non-violent software: you may only use, redistribute,
+ * and/or modify it under the terms of the CNPLv6+ as found in
+ * the LICENSE file in the source code root directory or at
+ * <https://git.pixie.town/thufie/CNPL>.
+ *
+ * libneo comes with ABSOLUTELY NO WARRANTY, to the extent
+ * permitted by applicable law.  See the CNPLv6+ for details.
+ */

src/string/string.cmake

@@ -1,3 +1,4 @@
 target_sources(neo PRIVATE
+    ./string/nstr.c
     ./string/utf.c
 )