From 28f2fa3fd58b128ce02142305f6074bed407019e Mon Sep 17 00:00:00 2001
From: behzad nouri <behzadnouri@gmail.com>
Date: Wed, 9 Sep 2020 15:28:17 +0000
Subject: [PATCH] uses rust intrinsics to convert hashes to u64 (#12097)

---
 core/Cargo.toml                  |  3 +++
 core/benches/crds_gossip_pull.rs | 26 ++++++++++++++++++++++++
 core/src/crds_gossip_pull.rs     | 34 ++++++++++++++++++++++++++------
 3 files changed, 57 insertions(+), 6 deletions(-)
 create mode 100644 core/benches/crds_gossip_pull.rs

diff --git a/core/Cargo.toml b/core/Cargo.toml
index cb2427c836..2eac2a2c66 100644
--- a/core/Cargo.toml
+++ b/core/Cargo.toml
@@ -94,6 +94,9 @@ name = "banking_stage"
 [[bench]]
 name = "blockstore"
 
+[[bench]]
+name = "crds_gossip_pull"
+
 [[bench]]
 name = "gen_keys"
 
diff --git a/core/benches/crds_gossip_pull.rs b/core/benches/crds_gossip_pull.rs
new file mode 100644
index 0000000000..d040266a8f
--- /dev/null
+++ b/core/benches/crds_gossip_pull.rs
@@ -0,0 +1,26 @@
+#![feature(test)]
+
+extern crate test;
+
+use rand::{thread_rng, Rng};
+use solana_core::crds_gossip_pull::CrdsFilter;
+use solana_sdk::hash::{Hash, HASH_BYTES};
+use test::Bencher;
+
+#[bench]
+fn bench_hash_as_u64(bencher: &mut Bencher) {
+    let mut rng = thread_rng();
+    let hashes: Vec<_> = (0..1000)
+        .map(|_| {
+            let mut buf = [0u8; HASH_BYTES];
+            rng.fill(&mut buf);
+            Hash::new(&buf)
+        })
+        .collect();
+    bencher.iter(|| {
+        hashes
+            .iter()
+            .map(CrdsFilter::hash_as_u64)
+            .collect::<Vec<_>>()
+    });
+}
diff --git a/core/src/crds_gossip_pull.rs b/core/src/crds_gossip_pull.rs
index 5fdda80e42..946fee1a1a 100644
--- a/core/src/crds_gossip_pull.rs
+++ b/core/src/crds_gossip_pull.rs
@@ -22,6 +22,7 @@ use solana_sdk::pubkey::Pubkey;
 use std::cmp;
 use std::collections::VecDeque;
 use std::collections::{HashMap, HashSet};
+use std::convert::TryInto;
 
 pub const CRDS_GOSSIP_PULL_CRDS_TIMEOUT_MS: u64 = 15000;
 // The maximum age of a value received over pull responses
@@ -74,12 +75,8 @@ impl CrdsFilter {
         ((num_items / max_items).log2().ceil()).max(0.0) as u32
     }
     pub fn hash_as_u64(item: &Hash) -> u64 {
-        let arr = item.as_ref();
-        let mut accum = 0;
-        for (i, val) in arr.iter().enumerate().take(8) {
-            accum |= (u64::from(*val)) << (i * 8) as u64;
-        }
-        accum
+        let buf = item.as_ref()[..8].try_into().unwrap();
+        u64::from_le_bytes(buf)
     }
     pub fn test_mask_u64(&self, item: u64, ones: u64) -> bool {
         let bits = item | ones;
@@ -543,6 +540,31 @@ mod test {
     use solana_sdk::hash::{hash, HASH_BYTES};
     use solana_sdk::packet::PACKET_DATA_SIZE;
 
+    #[test]
+    fn test_hash_as_u64() {
+        let arr: Vec<u8> = (0..HASH_BYTES).map(|i| i as u8 + 1).collect();
+        let hash = Hash::new(&arr);
+        assert_eq!(CrdsFilter::hash_as_u64(&hash), 0x807060504030201);
+    }
+
+    #[test]
+    fn test_hash_as_u64_random() {
+        fn hash_as_u64_bitops(hash: &Hash) -> u64 {
+            let mut out = 0;
+            for (i, val) in hash.as_ref().iter().enumerate().take(8) {
+                out |= (u64::from(*val)) << (i * 8) as u64;
+            }
+            out
+        }
+        let mut rng = thread_rng();
+        for _ in 0..100 {
+            let mut buf = [0u8; HASH_BYTES];
+            rng.fill(&mut buf);
+            let hash = Hash::new(&buf);
+            assert_eq!(CrdsFilter::hash_as_u64(&hash), hash_as_u64_bitops(&hash));
+        }
+    }
+
     #[test]
     fn test_new_pull_with_stakes() {
         let mut crds = Crds::default();