wip varint

src/test_main.zig

@@ -5,4 +5,5 @@ test "turbonss test suite" {
     _ = @import("user.zig");
     _ = @import("group.zig");
     _ = @import("padding.zig");
+    _ = @import("varint.zig");
 }

src/varint.zig

@@ -0,0 +1,90 @@
+//
+// varint64 []const u8 variants
+//
+// Thanks to https://github.com/gsquire/zig-snappy/blob/master/snappy.zig and golang's
+// varint implementation.
+
+const std = @import("std");
+
+// Represents a variable length integer that we read from a byte stream along
+// with how many bytes were read to decode it.
+pub const Varint = struct {
+    value: u64,
+    bytesRead: usize,
+};
+
+const MaxVarintLen64 = 10;
+
+// https://golang.org/pkg/encoding/binary/#Uvarint
+pub fn uvarint(buf: []const u8) error{Overflow}!Varint {
+    var x: u64 = 0;
+    var s: u6 = 0;
+
+    for (buf) |b, i| {
+        if (i == MaxVarintLen64) {
+            // Catch byte reads past MaxVarintLen64.
+            // See issue https://golang.org/issues/41185
+            return error.Overflow;
+        }
+
+        if (b < 0x80) {
+            if (i == MaxVarintLen64 - 1 and b > 1) {
+                return error.Overflow;
+            }
+            return Varint{ .value = x | (@as(u64, b) << s), .bytesRead = i + 1 };
+        }
+        x |= (@as(u64, b & 0x7f) << s);
+        s += 7;
+    }
+
+    return Varint{
+        .value = 0,
+        .bytesRead = 0,
+    };
+}
+
+// https://golang.org/pkg/encoding/binary/#PutUvarint
+pub fn putUvarint(buf: []u8, x: u64) usize {
+    var i: usize = 0;
+    var mutX = x;
+
+    while (mutX >= 0x80) {
+        buf[i] = @truncate(u8, mutX) | 0x80;
+        mutX >>= 7;
+        i += 1;
+    }
+    buf[i] = @truncate(u8, mutX);
+
+    return i + 1;
+}
+
+const testing = std.testing;
+
+const tests = [_]u64{
+    0,
+    1,
+    2,
+    10,
+    20,
+    63,
+    64,
+    65,
+    127,
+    128,
+    129,
+    255,
+    256,
+    257,
+    1 << 63 - 1,
+};
+
+test "uvarint" {
+    for (tests) |x| {
+        var buf: [MaxVarintLen64]u8 = undefined;
+        const n = putUvarint(buf[0..], x);
+        const got = try uvarint(buf[0..n]);
+
+        try testing.expectEqual(x, got.value);
+        try testing.expectEqual(n, got.bytesRead);
+    }
+}