Support more than 64 CPU features.
After recent patches, we have exactly 64 CPU features. This patch makes
the mechanism flexible so that we can support more features in the
future.
Several operators on CPUFeatures had to be re-written as part of this,
so this patch replaces the default-argument implementations with a more
flexible template-based approach, which can accept more than four
features. Existing usage remains unaffected.
Change-Id: If91a3adb62669aa827464e857a90eb93a64db7a6
diff --git a/src/cpu-features.h b/src/cpu-features.h
index 738fa69..1b0f2c2 100644
--- a/src/cpu-features.h
+++ b/src/cpu-features.h
@@ -27,6 +27,7 @@
#ifndef VIXL_CPU_FEATURES_H
#define VIXL_CPU_FEATURES_H
+#include <bitset>
#include <ostream>
#include "globals-vixl.h"
@@ -262,13 +263,13 @@
// clang-format on
// By default, construct with no features enabled.
- CPUFeatures() : features_(0) {}
+ CPUFeatures() : features_{} {}
// Construct with some features already enabled.
- CPUFeatures(Feature feature0,
- Feature feature1 = kNone,
- Feature feature2 = kNone,
- Feature feature3 = kNone);
+ template <typename T, typename... U>
+ CPUFeatures(T first, U... others) : features_{} {
+ Combine(first, others...);
+ }
// Construct with all features enabled. This can be used to disable feature
// checking: `Has(...)` returns true regardless of the argument.
@@ -301,41 +302,59 @@
// exist in this set are left unchanged.
void Combine(const CPUFeatures& other);
- // Combine specific features into this set. Features that already exist in
- // this set are left unchanged.
- void Combine(Feature feature0,
- Feature feature1 = kNone,
- Feature feature2 = kNone,
- Feature feature3 = kNone);
+ // Combine a specific feature into this set. If it already exists in the set,
+ // the set is left unchanged.
+ void Combine(Feature feature);
+
+ // Combine multiple features (or feature sets) into this set.
+ template <typename T, typename... U>
+ void Combine(T first, U... others) {
+ Combine(first);
+ Combine(others...);
+ }
// Remove features in another CPUFeatures object from this one.
void Remove(const CPUFeatures& other);
- // Remove specific features from this set.
- void Remove(Feature feature0,
- Feature feature1 = kNone,
- Feature feature2 = kNone,
- Feature feature3 = kNone);
+ // Remove a specific feature from this set. This has no effect if the feature
+ // doesn't exist in the set.
+ void Remove(Feature feature0);
- // Chaining helpers for convenient construction.
- CPUFeatures With(const CPUFeatures& other) const;
- CPUFeatures With(Feature feature0,
- Feature feature1 = kNone,
- Feature feature2 = kNone,
- Feature feature3 = kNone) const;
- CPUFeatures Without(const CPUFeatures& other) const;
- CPUFeatures Without(Feature feature0,
- Feature feature1 = kNone,
- Feature feature2 = kNone,
- Feature feature3 = kNone) const;
+ // Remove multiple features (or feature sets) from this set.
+ template <typename T, typename... U>
+ void Remove(T first, U... others) {
+ Remove(first);
+ Remove(others...);
+ }
- // Query features.
- // Note that an empty query (like `Has(kNone)`) always returns true.
+ // Chaining helpers for convenient construction by combining other CPUFeatures
+ // or individual Features.
+ template <typename... T>
+ CPUFeatures With(T... others) const {
+ CPUFeatures f(*this);
+ f.Combine(others...);
+ return f;
+ }
+
+ template <typename... T>
+ CPUFeatures Without(T... others) const {
+ CPUFeatures f(*this);
+ f.Remove(others...);
+ return f;
+ }
+
+ // Test whether the `other` feature set is equal to or a subset of this one.
bool Has(const CPUFeatures& other) const;
- bool Has(Feature feature0,
- Feature feature1 = kNone,
- Feature feature2 = kNone,
- Feature feature3 = kNone) const;
+
+ // Test whether a single feature exists in this set.
+ // Note that `Has(kNone)` always returns true.
+ bool Has(Feature feature) const;
+
+ // Test whether all of the specified features exist in this set.
+ template <typename T, typename... U>
+ bool Has(T first, U... others) const {
+ return Has(first) && Has(others...);
+ }
// Return the number of enabled features.
size_t Count() const;
@@ -353,9 +372,8 @@
const_iterator end() const;
private:
- // Each bit represents a feature. This field will be replaced as needed if
- // features are added.
- uint64_t features_;
+ // Each bit represents a feature. This set will be extended as needed.
+ std::bitset<kNumberOfFeatures> features_;
friend std::ostream& operator<<(std::ostream& os,
const vixl::CPUFeatures& features);
@@ -424,21 +442,17 @@
// Start a CPUFeaturesScope on any object that implements
// `CPUFeatures* GetCPUFeatures()`.
template <typename T>
- explicit CPUFeaturesScope(T* cpu_features_wrapper,
- CPUFeatures::Feature feature0 = CPUFeatures::kNone,
- CPUFeatures::Feature feature1 = CPUFeatures::kNone,
- CPUFeatures::Feature feature2 = CPUFeatures::kNone,
- CPUFeatures::Feature feature3 = CPUFeatures::kNone)
+ explicit CPUFeaturesScope(T* cpu_features_wrapper)
: cpu_features_(cpu_features_wrapper->GetCPUFeatures()),
- old_features_(*cpu_features_) {
- cpu_features_->Combine(feature0, feature1, feature2, feature3);
- }
+ old_features_(*cpu_features_) {}
- template <typename T>
- CPUFeaturesScope(T* cpu_features_wrapper, const CPUFeatures& other)
+ // Start a CPUFeaturesScope on any object that implements
+ // `CPUFeatures* GetCPUFeatures()`, with the specified features enabled.
+ template <typename T, typename U, typename... V>
+ CPUFeaturesScope(T* cpu_features_wrapper, U first, V... features)
: cpu_features_(cpu_features_wrapper->GetCPUFeatures()),
old_features_(*cpu_features_) {
- cpu_features_->Combine(other);
+ cpu_features_->Combine(first, features...);
}
~CPUFeaturesScope() { *cpu_features_ = old_features_; }