1 files changed, 108 insertions, 0 deletions
diff --git a/bin/edi/iter.c b/bin/edi/iter.c
new file mode 100644
index 00000000..a4c97b71
--- /dev/null
+++ b/bin/edi/iter.c
@@ -0,0 +1,108 @@
+/* Copyright (C) 2018  Curtis McEnroe <june@causal.agency>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdlib.h>
+#include <wchar.h>
+
+#include "edi.h"
+
+struct Iter iter(const struct Table *table, size_t at) {
+	struct Span span = { 0, 0 };
+	size_t slice;
+	for (slice = 0; slice < table->len; ++slice) {
+		span = spanNext(span, table->slices[slice].len);
+		if (span.at <= at && span.to > at) break;
+	}
+	return (struct Iter) {
+		.table = table,
+		.span = span,
+		.slice = slice,
+		.at = (at < span.to ? at : span.to),
+		.ch = (at < span.to ? table->slices[slice].ptr[at - span.at] : WEOF),
+	};
+}
+
+struct Iter iterNext(struct Iter it) {
+	if (it.at == it.span.to && it.ch == WEOF) return it;
+	it.at++;
+	if (it.at == it.span.to) {
+		if (it.slice + 1 == it.table->len) {
+			it.ch = WEOF;
+			return it;
+		}
+		it.slice++;
+		it.span = spanNext(it.span, it.table->slices[it.slice].len);
+	}
+	it.ch = it.table->slices[it.slice].ptr[it.at - it.span.at];
+	return it;
+}
+
+struct Iter iterPrev(struct Iter it) {
+	if (it.at > it.span.to && it.ch == WEOF) return it;
+	it.at--;
+	if (it.at > it.span.to) {
+		it.ch = WEOF;
+		return it;
+	}
+	if (it.at < it.span.at) {
+		it.slice--;
+		it.span = spanPrev(it.span, it.table->slices[it.slice].len);
+	}
+	it.ch = it.table->slices[it.slice].ptr[it.at - it.span.at];
+	return it;
+}
+
+#ifdef TEST
+#include <assert.h>
+
+int main() {
+	struct Slice slices[2] = {
+		{ L"AB", 2 },
+		{ L"CD", 2 },
+	};
+	struct Table table = { .len = 2, .slices = slices };
+
+	assert(L'A' == iter(&table, 0).ch);
+	assert(L'B' == iter(&table, 1).ch);
+	assert(L'C' == iter(&table, 2).ch);
+	assert(L'D' == iter(&table, 3).ch);
+
+	assert(L'B' == iterNext(iter(&table, 0)).ch);
+	assert(L'C' == iterNext(iter(&table, 1)).ch);
+	assert(L'D' == iterNext(iter(&table, 2)).ch);
+	assert(WEOF == iterNext(iter(&table, 5)).ch);
+
+	assert(WEOF == iterPrev(iter(&table, 0)).ch);
+	assert(L'A' == iterPrev(iter(&table, 1)).ch);
+	assert(L'B' == iterPrev(iter(&table, 2)).ch);
+	assert(L'C' == iterPrev(iter(&table, 3)).ch);
+
+	struct Iter it = iter(&table, 3);
+	it = iterNext(it);
+	it = iterNext(it);
+	assert(WEOF == it.ch);
+	it = iterPrev(it);
+	assert(L'D' == it.ch);
+
+	it = iter(&table, 0);
+	it = iterPrev(it);
+	it = iterPrev(it);
+	assert(WEOF == it.ch);
+	it = iterNext(it);
+	assert(L'A' == it.ch);
+}
+
+#endif