/usr/include/quagga/checksum.h is in quagga 0.99.20.1-0ubuntu0.12.04.6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | extern int in_cksum(void *, int);
extern u_int16_t fletcher_checksum(u_char *, const size_t len, const uint16_t offset);
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