mirror of
https://github.com/facebook/react-native.git
synced 2025-11-01 09:14:26 +00:00
Samuel Susla
81a97de546
Summary:
changelog: [internal]
Prevents 2 type converions:
1. int <-> size_t
2. int <-> int32_t
# Why is using size_t better when working with indexes.
## 1. Type conversion isn't for free.
Take this example
```
size_t calculate(int number) {
return number + 1;
}
```
It generates following assembly (generated with armv8-a clang 10.0.0):
```
calculate(int): // calculate(int)
sub sp, sp, #16 // =16
str w0, [sp, #12]
ldr w8, [sp, #12]
add w9, w8, #1 // =1
mov w8, w9
sxtw x0, w8
add sp, sp, #16 // =16
ret
```
That's 9 instructions.
If we get rid of type conversion:
```
size_t calculate(size_t number) {
return number + 1;
}
```
Assembly (generated with armv8-a clang 10.0.0):
```
calculate(unsigned long): // calculate(unsigned long)
sub sp, sp, #16 // =16
str x0, [sp, #8]
ldr x8, [sp, #8]
add x0, x8, #1 // =1
add sp, sp, #16 // =16
ret
```
Compiler now produces only 7 instructions.
## Semantics
When using int for indexing, the type doesn't say much. By using `size_t`, just by looking at the type, it gives the reader more information about where it is coming from.
Reviewed By: JoshuaGross
Differential Revision: D24332248
fbshipit-source-id: 87ef982829ec14906ed9e002ea2e875fda4a0cd8
103 lines
2.5 KiB
C++
103 lines
2.5 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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#pragma once
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#include <better/small_vector.h>
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#include <folly/Hash.h>
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#include <react/renderer/core/EventEmitter.h>
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#include <react/renderer/core/LayoutMetrics.h>
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#include <react/renderer/core/Props.h>
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#include <react/renderer/core/ReactPrimitives.h>
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#include <react/renderer/core/ShadowNode.h>
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namespace facebook {
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namespace react {
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/*
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* Describes a view that can be mounted.
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* This is exposed to the mounting layer.
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*/
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struct ShadowView final {
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ShadowView() = default;
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ShadowView(ShadowView const &shadowView) = default;
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ShadowView(ShadowView &&shadowView) noexcept = default;
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/*
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* Constructs a `ShadowView` from given `ShadowNode`.
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*/
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explicit ShadowView(ShadowNode const &shadowNode);
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ShadowView &operator=(ShadowView const &other) = default;
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ShadowView &operator=(ShadowView &&other) = default;
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bool operator==(ShadowView const &rhs) const;
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bool operator!=(ShadowView const &rhs) const;
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ComponentName componentName{};
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ComponentHandle componentHandle{};
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Tag tag{};
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Props::Shared props{};
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EventEmitter::Shared eventEmitter{};
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LayoutMetrics layoutMetrics{EmptyLayoutMetrics};
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State::Shared state{};
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};
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#if RN_DEBUG_STRING_CONVERTIBLE
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std::string getDebugName(ShadowView const &object);
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std::vector<DebugStringConvertibleObject> getDebugProps(
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ShadowView const &object,
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DebugStringConvertibleOptions options);
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#endif
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/*
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* Describes pair of a `ShadowView` and a `ShadowNode`.
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* This is not exposed to the mounting layer.
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*
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*/
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struct ShadowViewNodePair final {
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using List = better::
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small_vector<ShadowViewNodePair, kShadowNodeChildrenSmallVectorSize>;
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ShadowView shadowView;
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ShadowNode const *shadowNode;
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bool flattened{false};
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bool isConcreteView{true};
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size_t mountIndex{0};
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bool inOtherTree{false};
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/*
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* The stored pointer to `ShadowNode` represents an identity of the pair.
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*/
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bool operator==(const ShadowViewNodePair &rhs) const;
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bool operator!=(const ShadowViewNodePair &rhs) const;
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};
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} // namespace react
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} // namespace facebook
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namespace std {
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template <>
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struct hash<facebook::react::ShadowView> {
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size_t operator()(const facebook::react::ShadowView &shadowView) const {
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return folly::hash::hash_combine(
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0,
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shadowView.componentHandle,
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shadowView.tag,
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shadowView.props,
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shadowView.eventEmitter,
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shadowView.state);
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}
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};
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} // namespace std
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