Unroll checksum computation loop.

Checksum computation is one of the most expensive bits of
packet processing. Manual unrolling of the loop provides
significant improvement in checksum speed.

Updates #1656

BenchmarkChecksum/checksum_64-12                49834124                23.6 ns/op
BenchmarkChecksum/checksum_128-12               27111997                44.1 ns/op
BenchmarkChecksum/checksum_256-12               11416683                91.5 ns/op
BenchmarkChecksum/checksum_512-12                6375298               174 ns/op
BenchmarkChecksum/checksum_1024-12               3403852               338 ns/op
BenchmarkChecksum/checksum_1500-12               2343576               493 ns/op
BenchmarkChecksum/checksum_2048-12               1730521               656 ns/op
BenchmarkChecksum/checksum_4096-12                920469              1327 ns/op
BenchmarkChecksum/checksum_8192-12                445885              2637 ns/op
BenchmarkChecksum/checksum_16384-12               226342              5268 ns/op
BenchmarkChecksum/checksum_32767-12               114210             10503 ns/op
BenchmarkChecksum/checksum_32768-12                99138             10610 ns/op
BenchmarkChecksum/checksum_65535-12                53438             21158 ns/op
BenchmarkChecksum/checksum_65536-12                52993             21067 ns/op
BenchmarkUnrolledChecksum/checksum_64-12        61035639                19.1 ns/op
BenchmarkUnrolledChecksum/checksum_128-12               36067015                33.6 ns/op
BenchmarkUnrolledChecksum/checksum_256-12               19731220                60.4 ns/op
BenchmarkUnrolledChecksum/checksum_512-12                9091291               116 ns/op
BenchmarkUnrolledChecksum/checksum_1024-12               4976406               226 ns/op
BenchmarkUnrolledChecksum/checksum_1500-12               3685224               328 ns/op
BenchmarkUnrolledChecksum/checksum_2048-12               2579108               447 ns/op
BenchmarkUnrolledChecksum/checksum_4096-12               1350475               887 ns/op
BenchmarkUnrolledChecksum/checksum_8192-12                658248              1780 ns/op
BenchmarkUnrolledChecksum/checksum_16384-12               335869              3534 ns/op
BenchmarkUnrolledChecksum/checksum_32767-12               168650              7095 ns/op
BenchmarkUnrolledChecksum/checksum_32768-12               168075              7098 ns/op
BenchmarkUnrolledChecksum/checksum_65535-12                75085             14277 ns/op
BenchmarkUnrolledChecksum/checksum_65536-12                75921             14127 ns/op

PiperOrigin-RevId: 291643290

0 files changed, 0 insertions, 0 deletions