expose `len` to the delta-compressed iterator

src/compress.zig

@@ -102,14 +102,20 @@ const varintSliceIterator = struct {
     arr: []const u8,
     idx: usize,
 
-    pub fn next(it: *varintSliceIterator) error{Overflow}!?u64 {
-        if (it.remaining == 0)
+    pub fn next(self: *varintSliceIterator) error{Overflow}!?u64 {
+        if (self.remaining == 0)
             return null;
-        const value = try uvarint(it.arr[it.idx..]);
-        it.idx += value.bytes_read;
-        it.remaining -= 1;
+        const value = try uvarint(self.arr[self.idx..]);
+        self.idx += value.bytes_read;
+        self.remaining -= 1;
         return value.value;
     }
+
+    // returns the number of remaining items. If called before the first
+    // next(), returns the length of the slice.
+    pub fn remaining(self: *const varintSliceIterator) usize {
+        return self.remaining;
+    }
 };
 
 pub fn VarintSliceIterator(arr: []const u8) error{Overflow}!varintSliceIterator {
@@ -126,16 +132,22 @@ const deltaDecompressionIterator = struct {
     prev: u64,
     add_to_prev: u1,
 
-    pub fn next(it: *deltaDecompressionIterator) error{Overflow}!?u64 {
-        const current = try it.vit.next();
+    pub fn next(self: *deltaDecompressionIterator) error{Overflow}!?u64 {
+        const current = try self.vit.next();
         if (current == null) return null;
 
-        const prevExtra = try math.add(u64, it.prev, it.add_to_prev);
+        const prevExtra = try math.add(u64, self.prev, self.add_to_prev);
         const result = try math.add(u64, current.?, prevExtra);
-        it.prev = result;
-        it.add_to_prev = 1;
+        self.prev = result;
+        self.add_to_prev = 1;
         return result;
     }
+
+    // returns the number of remaining items. If called before the first
+    // next(), returns the length of the slice.
+    pub fn remaining(self: *const deltaDecompressionIterator) usize {
+        return self.vit.remaining;
+    }
 };
 
 pub fn DeltaDecompressionIterator(vit: *varintSliceIterator) deltaDecompressionIterator {
@@ -257,10 +269,9 @@ test "delta decompress overflow" {
 }
 
 test "delta decompression with an iterator" {
-    const allocator = testing.allocator;
-    var compressed = try testing.allocator.dupe(u64, uvarint_tests[0..]);
-    defer allocator.free(compressed);
-    try deltaCompress(u64, compressed);
+    var compressed: [uvarint_tests.len]u64 = undefined;
+    std.mem.copy(u64, compressed[0..], uvarint_tests[0..]);
+    try deltaCompress(u64, compressed[0..]);
 
     var buf = ArrayList(u8).init(testing.allocator);
     defer buf.deinit();
@@ -270,6 +281,7 @@ test "delta decompression with an iterator" {
 
     var it = DeltaDecompressionIterator(&try VarintSliceIterator(buf.items));
     var i: usize = 0;
+    try testing.expectEqual(it.remaining(), uvarint_tests.len);
     while (try it.next()) |got| : (i += 1) {
         try testing.expectEqual(uvarint_tests[i], got);
     }