Merge #13258: uint256: Remove unnecessary crypto/common.h dependency

bf2e01097 uint256: Remove unnecessary crypto/common.h use (Karl-Johan Alm)

Pull request description:

  This is an alternative to #13242 which keeps the `ReadLE64` part, but moves the `crypto/common.h` dependency into `crypto/common.h` as a function outside of `uint256`.

  **Reason:** this change will remove dependencies for `uint256` to `crypto/common.h`, `compat/endian.h`, and `compat/byteswap.h`.

  This PR removes the need to update tests to be endian-aware/-independent, but keeps the (arguably dubious) `ReadLE64` part (which was only introduced to fix the tests, not for any functionality).

Tree-SHA512: 78b35123cdb185b3b3ec59aba5ca8a5db72624d147f2d6a5484ffa5ce626a72f782a01dc6893fc8f5619b03e2eae7b5a03b0df5d43460f3bda428e719e188aec

src/addrman.cpp

@@ -11,22 +11,22 @@
 
 int CAddrInfo::GetTriedBucket(const uint256& nKey) const
 {
-    uint64_t hash1 = (CHashWriter(SER_GETHASH, 0) << nKey << GetKey()).GetHash().GetCheapHash();
-    uint64_t hash2 = (CHashWriter(SER_GETHASH, 0) << nKey << GetGroup() << (hash1 % ADDRMAN_TRIED_BUCKETS_PER_GROUP)).GetHash().GetCheapHash();
+    uint64_t hash1 = (CHashWriter(SER_GETHASH, 0) << nKey << GetKey()).GetCheapHash();
+    uint64_t hash2 = (CHashWriter(SER_GETHASH, 0) << nKey << GetGroup() << (hash1 % ADDRMAN_TRIED_BUCKETS_PER_GROUP)).GetCheapHash();
     return hash2 % ADDRMAN_TRIED_BUCKET_COUNT;
 }
 
 int CAddrInfo::GetNewBucket(const uint256& nKey, const CNetAddr& src) const
 {
     std::vector<unsigned char> vchSourceGroupKey = src.GetGroup();
-    uint64_t hash1 = (CHashWriter(SER_GETHASH, 0) << nKey << GetGroup() << vchSourceGroupKey).GetHash().GetCheapHash();
-    uint64_t hash2 = (CHashWriter(SER_GETHASH, 0) << nKey << vchSourceGroupKey << (hash1 % ADDRMAN_NEW_BUCKETS_PER_SOURCE_GROUP)).GetHash().GetCheapHash();
+    uint64_t hash1 = (CHashWriter(SER_GETHASH, 0) << nKey << GetGroup() << vchSourceGroupKey).GetCheapHash();
+    uint64_t hash2 = (CHashWriter(SER_GETHASH, 0) << nKey << vchSourceGroupKey << (hash1 % ADDRMAN_NEW_BUCKETS_PER_SOURCE_GROUP)).GetCheapHash();
     return hash2 % ADDRMAN_NEW_BUCKET_COUNT;
 }
 
 int CAddrInfo::GetBucketPosition(const uint256 &nKey, bool fNew, int nBucket) const
 {
-    uint64_t hash1 = (CHashWriter(SER_GETHASH, 0) << nKey << (fNew ? 'N' : 'K') << nBucket << GetKey()).GetHash().GetCheapHash();
+    uint64_t hash1 = (CHashWriter(SER_GETHASH, 0) << nKey << (fNew ? 'N' : 'K') << nBucket << GetKey()).GetCheapHash();
     return hash1 % ADDRMAN_BUCKET_SIZE;
 }
 

src/hash.h

@@ -6,6 +6,7 @@
 #ifndef BITCOIN_HASH_H
 #define BITCOIN_HASH_H
 
+#include <crypto/common.h>
 #include <crypto/ripemd160.h>
 #include <crypto/sha256.h>
 #include <prevector.h>
@@ -138,6 +139,15 @@ public:
         return result;
     }
 
+    /**
+     * Returns the first 64 bits from the resulting hash.
+     */
+    inline uint64_t GetCheapHash() {
+        unsigned char result[CHash256::OUTPUT_SIZE];
+        ctx.Finalize(result);
+        return ReadLE64(result);
+    }
+
     template<typename T>
     CHashWriter& operator<<(const T& obj) {
         // Serialize to this stream

src/test/addrman_tests.cpp

@@ -34,7 +34,7 @@ public:
 
     int RandomInt(int nMax) override
     {
-        state = (CHashWriter(SER_GETHASH, 0) << state).GetHash().GetCheapHash();
+        state = (CHashWriter(SER_GETHASH, 0) << state).GetCheapHash();
         return (unsigned int)(state % nMax);
     }
 

src/uint256.h

@@ -12,7 +12,6 @@
 #include <stdint.h>
 #include <string>
 #include <vector>
-#include <crypto/common.h>
 
 /** Template base class for fixed-sized opaque blobs. */
 template<unsigned int BITS>
@@ -123,16 +122,6 @@ class uint256 : public base_blob<256> {
 public:
     uint256() {}
     explicit uint256(const std::vector<unsigned char>& vch) : base_blob<256>(vch) {}
-
-    /** A cheap hash function that just returns 64 bits from the result, it can be
-     * used when the contents are considered uniformly random. It is not appropriate
-     * when the value can easily be influenced from outside as e.g. a network adversary could
-     * provide values to trigger worst-case behavior.
-     */
-    uint64_t GetCheapHash() const
-    {
-        return ReadLE64(data);
-    }
 };
 
 /* uint256 from const char *.

src/validation.h

@@ -12,6 +12,7 @@
 
 #include <amount.h>
 #include <coins.h>
+#include <crypto/common.h> // for ReadLE64
 #include <fs.h>
 #include <protocol.h> // For CMessageHeader::MessageStartChars
 #include <policy/feerate.h>
@@ -138,7 +139,10 @@ static const int DEFAULT_STOPATHEIGHT = 0;
 
 struct BlockHasher
 {
-    size_t operator()(const uint256& hash) const { return hash.GetCheapHash(); }
+    // this used to call `GetCheapHash()` in uint256, which was later moved; the
+    // cheap hash function simply calls ReadLE64() however, so the end result is
+    // identical
+    size_t operator()(const uint256& hash) const { return ReadLE64(hash.begin()); }
 };
 
 extern CScript COINBASE_FLAGS;