1 // Copyright 2021 The Abseil Authors
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 #ifndef ABSL_STRINGS_INTERNAL_CORD_REP_CRC_H_
16 #define ABSL_STRINGS_INTERNAL_CORD_REP_CRC_H_
17
18 #include <cassert>
19 #include <cstdint>
20
21 #include "absl/base/config.h"
22 #include "absl/base/optimization.h"
23 #include "absl/crc/internal/crc_cord_state.h"
24 #include "absl/strings/internal/cord_internal.h"
25
26 namespace absl {
27 ABSL_NAMESPACE_BEGIN
28 namespace cord_internal {
29
30 // CordRepCrc is a CordRep node intended only to appear at the top level of a
31 // cord tree. It associates an "expected CRC" with the contained data, to allow
32 // for easy passage of checksum data in Cord data flows.
33 //
34 // From Cord's perspective, the crc value has no semantics; any validation of
35 // the contained checksum is the user's responsibility.
36 struct CordRepCrc : public CordRep {
37 CordRep* child;
38 absl::crc_internal::CrcCordState crc_cord_state;
39
40 // Consumes `child` and returns a CordRepCrc prefixed tree containing `child`.
41 // If the specified `child` is itself a CordRepCrc node, then this method
42 // either replaces the existing node, or directly updates the crc state in it
43 // depending on the node being shared or not, i.e.: refcount.IsOne().
44 // `child` must only be null if the Cord is empty. Never returns null.
45 static CordRepCrc* New(CordRep* child, crc_internal::CrcCordState state);
46
47 // Destroys (deletes) the provided node. `node` must not be null.
48 static void Destroy(CordRepCrc* node);
49 };
50
51 // Consumes `rep` and returns a CordRep* with any outer CordRepCrc wrapper
52 // removed. This is usually a no-op (returning `rep`), but this will remove and
53 // unref an outer CordRepCrc node.
RemoveCrcNode(CordRep * rep)54 inline CordRep* RemoveCrcNode(CordRep* rep) {
55 assert(rep != nullptr);
56 if (ABSL_PREDICT_FALSE(rep->IsCrc())) {
57 CordRep* child = rep->crc()->child;
58 if (rep->refcount.IsOne()) {
59 delete rep->crc();
60 } else {
61 CordRep::Ref(child);
62 CordRep::Unref(rep);
63 }
64 return child;
65 }
66 return rep;
67 }
68
69 // Returns `rep` if it is not a CordRepCrc node, or its child if it is.
70 // Does not consume or create a reference on `rep` or the returned value.
SkipCrcNode(CordRep * rep)71 inline CordRep* SkipCrcNode(CordRep* rep) {
72 assert(rep != nullptr);
73 if (ABSL_PREDICT_FALSE(rep->IsCrc())) {
74 return rep->crc()->child;
75 } else {
76 return rep;
77 }
78 }
79
SkipCrcNode(const CordRep * rep)80 inline const CordRep* SkipCrcNode(const CordRep* rep) {
81 assert(rep != nullptr);
82 if (ABSL_PREDICT_FALSE(rep->IsCrc())) {
83 return rep->crc()->child;
84 } else {
85 return rep;
86 }
87 }
88
crc()89 inline CordRepCrc* CordRep::crc() {
90 assert(IsCrc());
91 return static_cast<CordRepCrc*>(this);
92 }
93
crc()94 inline const CordRepCrc* CordRep::crc() const {
95 assert(IsCrc());
96 return static_cast<const CordRepCrc*>(this);
97 }
98
99 } // namespace cord_internal
100 ABSL_NAMESPACE_END
101 } // namespace absl
102
103 #endif // ABSL_STRINGS_INTERNAL_CORD_REP_CRC_H_
104