Fix off-by-one error and notice that summing may need more than one
round for the result to be in the lower 16 bits.
---
src/libsystemd-dhcp/dhcp-client.c | 7 +++++--
src/libsystemd-dhcp/test-dhcp-client.c | 7 +++++--
2 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/src/libsystemd-dhcp/dhcp-client.c
b/src/libsystemd-dhcp/dhcp-client.c
index 7dc1546..68a3b1a 100644
--- a/src/libsystemd-dhcp/dhcp-client.c
+++ b/src/libsystemd-dhcp/dhcp-client.c
@@ -382,10 +382,13 @@ static uint16_t client_checksum(void *buf, int len)
if (len & 0x01) {
odd = buf;
- sum += odd[len];
+ sum += odd[len - 1];
}
- return ~((sum & 0xffff) + (sum >> 16));
+ while (sum >> 16)
+ sum = (sum & 0xffff) + (sum >> 16);
+
+ return ~sum;
}
static void client_append_ip_headers(DHCPPacket *packet, uint16_t len)
diff --git a/src/libsystemd-dhcp/test-dhcp-client.c
b/src/libsystemd-dhcp/test-dhcp-client.c
index d398510..7400cc6 100644
--- a/src/libsystemd-dhcp/test-dhcp-client.c
+++ b/src/libsystemd-dhcp/test-dhcp-client.c
@@ -102,10 +102,13 @@ static uint16_t client_checksum(void *buf, int len)
if (len & 0x01) {
odd = buf;
- sum += odd[len];
+ sum += odd[len - 1];
}
- return ~((sum & 0xffff) + (sum >> 16));
+ while (sum >> 16)
+ sum = (sum & 0xffff) + (sum >> 16);
+
+ return ~sum;
}
static void test_checksum(void)
--
1.7.10.4
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