From 18be89f6e87312edad7834cc0a0aef7d32739bc8 Mon Sep 17 00:00:00 2001
From: Conrad Hoffmann <ch@bitfehler.net>
Date: Mon, 14 Aug 2023 21:31:47 +0200
Subject: [PATCH] Fix checksum calculation and test it

Signed-off-by: Conrad Hoffmann <ch@bitfehler.net>
---
 net/icmp/+test.ha   |  5 +++++
 net/icmp/message.ha | 14 ++++++--------
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/net/icmp/+test.ha b/net/icmp/+test.ha
index fe79d92..0d4a5b6 100644
--- a/net/icmp/+test.ha
+++ b/net/icmp/+test.ha
@@ -18,6 +18,7 @@ use bytes;
 	let outbuf = memio::dynamic();
 	let encsz = encode(&outbuf, &inmsg)!;
 	assert(encsz == 13);
+	assert(inmsg.checksum == 8672);
 
 	let msg = memio::buffer(&outbuf);
 
@@ -60,6 +61,7 @@ use bytes;
 	let outbuf = memio::dynamic();
 	let encsz = encode(&outbuf, &inmsg)!;
 	assert(encsz == 13);
+	assert(inmsg.checksum == 10720);
 
 	let msg = memio::buffer(&outbuf);
 
@@ -98,6 +100,7 @@ use bytes;
 	let outbuf = memio::dynamic();
 	let encsz = encode(&outbuf, &inmsg)!;
 	assert(encsz == 4);
+	assert(inmsg.checksum == 64757);
 
 	let msg = memio::buffer(&outbuf);
 
@@ -129,6 +132,7 @@ use bytes;
 	let outbuf = memio::dynamic();
 	let encsz = encode(&outbuf, &inmsg)!;
 	assert(encsz == 4);
+	assert(inmsg.checksum == 62709);
 
 	let msg = memio::buffer(&outbuf);
 
@@ -161,6 +165,7 @@ use bytes;
 	let outbuf = memio::dynamic();
 	let encsz = encode(&outbuf, &inmsg)!;
 	assert(encsz == 6);
+	assert(inmsg.checksum == 62440);
 
 	let msg = memio::buffer(&outbuf);
 
diff --git a/net/icmp/message.ha b/net/icmp/message.ha
index cbeefeb..9e2c91f 100644
--- a/net/icmp/message.ha
+++ b/net/icmp/message.ha
@@ -56,21 +56,19 @@ fn checksum(msg: []u8) u16 = {
 	let cov: size = len(msg) - 1z;
 
 	let s: u32 = 0;
-	for (let i = 0z; i < cov; i += 1) {
-		s += ((msg[i + 1]: u32) << 8) | msg[i]: u32;
+	for (let i = 0z; i < cov; i += 2) {
+		s += ((msg[i]: u32) << 8) + msg[i + 1]: u32;
 	};
 
 	if (cov & 1 == 0) {
 		s += msg[cov]: u32;
 	};
 
-	s = (s >> 16) + (s & 0xffff);
-
-	s = s + (s >> 16);
-
-	s ^= s: u16;
+	for ((s >> 16) != 0) {
+		s = (s >> 16) + (s & 0xffff);
+	};
 
-	return s: u16;
+	return ~s: u16;
 };
 
 // Encodes a [[message]] into the [[io::handle]] provided
-- 
2.45.2