trie/bintrie: spec change, big endian hashing of slot key (#34670)

The spec has been changed during SIC #49, the offset is encoded as a
big-endian number.

Author: gballet

core/genesis_test.go

@@ -308,7 +308,7 @@ func TestVerkleGenesisCommit(t *testing.T) {
 		},
 	}
 
-	expected := common.FromHex("1fd154971d9a386c4ec75fe7138c17efb569bfc2962e46e94a376ba997e3fadc")
+	expected := common.FromHex("0870fd587c41dc778019de8c5cb3193fe4ef1f417976461952d3712ba39163f5")
 	got := genesis.ToBlock().Root().Bytes()
 	if !bytes.Equal(got, expected) {
 		t.Fatalf("invalid genesis state root, expected %x, got %x", expected, got)

trie/bintrie/key_encoding.go

@@ -54,15 +54,12 @@ func getBinaryTreeKey(addr common.Address, offset []byte, overflow bool) []byte
 	defer returnSha256(hasher)
 	hasher.Write(zeroHash[:12])
 	hasher.Write(addr[:])
-	var buf [32]byte
-	// key is big endian, hashed value is little endian
-	for i := range offset[:31] {
-		buf[i] = offset[30-i]
-	}
+	var buf [32]byte // TODO: make offset a 33-byte value to avoid an extra stack alloc
+	copy(buf[1:32], offset[:31])
 	if overflow {
 		// Overflow detected when adding MAIN_STORAGE_OFFSET,
 		// reporting it in the shifter 32 byte value.
-		buf[31] = 1
+		buf[0] = 1
 	}
 	hasher.Write(buf[:])
 	k := hasher.Sum(nil)