cipher-gcm-ppc: tweak loop structure a bit
* cipher/cipher-gcm-ppc.c (_gcry_ghash_ppc_vpmsum): Increament 'buf' pointer right after use; Use 'for' loop for inner 4-blocks loop to allow compiler to better optimize loop.
Benchmark on POWER9:
Before:
| nanosecs/byte mebibytes/sec cycles/byte
GMAC_AES | 0.226 ns/B 4211 MiB/s 0.521 c/B
After:
| nanosecs/byte mebibytes/sec cycles/byte
GMAC_AES | 0.224 ns/B 4251 MiB/s 0.516 c/B
- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>