Add GPU based PoH verification (#4524)

* Add GPU poh verify

* Switch to single PoH verify function

* Add EntrySlice verify tests with hashes and txs

* Add poh-verify benchmarks

core/benches/poh_verify.rs

@@ -0,0 +1,48 @@
+#![feature(test)]
+extern crate test;
+
+use solana::entry::EntrySlice;
+use solana::entry::{next_entry_mut, Entry};
+use solana_sdk::hash::{hash, Hash};
+use solana_sdk::signature::{Keypair, KeypairUtil};
+use solana_sdk::system_transaction;
+use test::Bencher;
+
+const NUM_HASHES: u64 = 400;
+const NUM_ENTRIES: usize = 800;
+
+#[bench]
+fn bench_poh_verify_ticks(bencher: &mut Bencher) {
+    let zero = Hash::default();
+    let mut cur_hash = hash(&zero.as_ref());
+    let start = *&cur_hash;
+
+    let mut ticks: Vec<Entry> = Vec::with_capacity(NUM_ENTRIES);
+    for _ in 0..NUM_ENTRIES {
+        ticks.push(next_entry_mut(&mut cur_hash, NUM_HASHES, vec![]));
+    }
+
+    bencher.iter(|| {
+        ticks.verify(&start);
+    })
+}
+
+#[bench]
+fn bench_poh_verify_transaction_entries(bencher: &mut Bencher) {
+    let zero = Hash::default();
+    let mut cur_hash = hash(&zero.as_ref());
+    let start = *&cur_hash;
+
+    let keypair1 = Keypair::new();
+    let pubkey1 = keypair1.pubkey();
+
+    let mut ticks: Vec<Entry> = Vec::with_capacity(NUM_ENTRIES);
+    for _ in 0..NUM_ENTRIES {
+        let tx = system_transaction::create_user_account(&keypair1, &pubkey1, 42, cur_hash);
+        ticks.push(next_entry_mut(&mut cur_hash, NUM_HASHES, vec![tx]));
+    }
+
+    bencher.iter(|| {
+        ticks.verify(&start);
+    })
+}