hare

commit e21766777dfbe21b88f913de04268419a5ee21bd
parent 3f685edba32354a9479a74cf7e7ae033bea037f7
Author: Bor Grošelj Simić <bor.groseljsimic@telemach.net>
Date:   Wed, 24 Feb 2021 00:55:56 +0100

bytes/index.ha: add rindex

Diffstat:
M
bytes/index.ha
 | 
46
++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 46 insertions(+), 0 deletions(-)
diff --git a/bytes/index.ha b/bytes/index.ha
@@ -24,6 +24,33 @@ fn index_slice(haystack: []u8, needle: []u8) (size | void) = {
 };
 
 
+// Returns the offset of the last instance of 'needle' in a 'haystack' of
+// bytes, or void if it is not found.
+export fn rindex(haystack: []u8, needle: (u8 | []u8)) (size | void) = {
+	return match (needle) {
+		b: u8   => rindex_byte(haystack, b),
+		b: []u8 => rindex_slice(haystack, b),
+	};
+};
+
+fn rindex_byte(haystack: []u8, needle: u8) (size | void) = {
+	for (let i = 0z; i < len(haystack); i += 1) {
+		if (haystack[len(haystack) - i - 1] == needle) {
+			return len(haystack) - i - 1;
+		};
+	};
+};
+
+fn rindex_slice(haystack: []u8, needle: []u8) (size | void) = {
+	for (let i = 0z; i + len(needle) <= len(haystack); i += 1) {
+		let r = len(haystack) - i;
+		if (equal(haystack[r - len(needle)..r], needle)) {
+			return r - len(needle);
+		};
+	};
+};
+
+
 @test fn index() void = {
 	// Bytes
 	const a: [4]u8 = [1, 3, 3, 7];
@@ -40,6 +67,20 @@ fn index_slice(haystack: []u8, needle: []u8) (size | void) = {
 		void => void,
 	};
 
+	match (rindex(a, 3)) {
+		n: size => assert(n == 2),
+		void => abort(),
+	};
+	match (rindex(a, 42)) {
+		n: size => abort(),
+		void => void,
+	};
+	match (rindex([], 42)) {
+		size => abort(),
+		void => void,
+	};
+
+
 	// Slices
 	match (index(a, [3, 3])) {
 		n: size => assert(n == 1),
@@ -59,4 +100,9 @@ fn index_slice(haystack: []u8, needle: []u8) (size | void) = {
 		n: size => assert(n == 1),
 		void => abort(),
 	};
+
+	match (rindex(special, [1, 1])) {
+		n: size => assert(n == 1),
+		void => abort(),
+	};
 };