From 1e6a350c3922eeb9c79ac14453399b6cab5a0b66 Mon Sep 17 00:00:00 2001
From: Altagos <jakob@altagos.dev>
Date: Fri, 5 Sep 2025 10:27:39 +0200
Subject: [PATCH] add zigzag coding
Change-Id: qvzvqruqmuwqywnwrsuoykzsmmnvpuxy

---
 src/ZigZag.zig | 37 +++++++++++++++++++++++++++++++++++++
 src/root.zig   |  1 +
 2 files changed, 38 insertions(+)
 create mode 100644 src/ZigZag.zig

diff --git a/src/ZigZag.zig b/src/ZigZag.zig
new file mode 100644
index 0000000..498237f
--- /dev/null
+++ b/src/ZigZag.zig
@@ -0,0 +1,37 @@
+pub fn encode(value: isize) usize {
+    if (value < 0) return @as(usize, @intCast(value * -1)) * 2 - 1;
+    return @as(usize, @intCast(value)) * 2;
+}
+
+pub fn decode(value: usize) isize {
+    if (value & 1 == 1) return -@as(isize, @intCast(value / 2)) - 1;
+    return @as(isize, @intCast(value / 2));
+}
+
+test "zigzag.encode val = 10" {
+    const testing = @import("std").testing;
+
+    const encoded = encode(10);
+    try testing.expectEqual(20, encoded);
+}
+
+test "zigzag.encode val = -42" {
+    const testing = @import("std").testing;
+
+    const encoded = encode(-42);
+    try testing.expectEqual(83, encoded);
+}
+
+test "zigzag.decode val = 20" {
+    const testing = @import("std").testing;
+
+    const decoded = decode(20);
+    try testing.expectEqual(10, decoded);
+}
+
+test "zigzag.decode val = 83" {
+    const testing = @import("std").testing;
+
+    const decoded = decode(83);
+    try testing.expectEqual(-42, decoded);
+}
diff --git a/src/root.zig b/src/root.zig
index 15e922a..b5afa98 100644
--- a/src/root.zig
+++ b/src/root.zig
@@ -2,6 +2,7 @@
 const std = @import("std");
 
 pub const Golomb = @import("Golomb.zig");
+pub const ZigZag = @import("ZigZag.zig");
 
 test {
     std.testing.refAllDecls(@This());
-- 
2.43.0