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//
// Copyright 2012 The Android Open Source Project
//
// Manage a resource ID cache.
#define LOG_TAG "ResourceIdCache"
#include <utils/String16.h>
#include <utils/Log.h>
#include "ResourceIdCache.h"
#include <map>
using namespace std;
static size_t mHits = 0;
static size_t mMisses = 0;
static size_t mCollisions = 0;
static const size_t MAX_CACHE_ENTRIES = 2048;
static const android::String16 TRUE16("1");
static const android::String16 FALSE16("0");
struct CacheEntry {
// concatenation of the relevant strings into a single instance
android::String16 hashedName;
uint32_t id;
CacheEntry() {}
CacheEntry(const android::String16& name, uint32_t resId) : hashedName(name), id(resId) { }
};
static map< uint32_t, CacheEntry > mIdMap;
// djb2; reasonable choice for strings when collisions aren't particularly important
static inline uint32_t hashround(uint32_t hash, int c) {
return ((hash << 5) + hash) + c; /* hash * 33 + c */
}
static uint32_t hash(const android::String16& hashableString) {
uint32_t hash = 5381;
const char16_t* str = hashableString.string();
while (int c = *str++) hash = hashround(hash, c);
return hash;
}
namespace android {
static inline String16 makeHashableName(const android::String16& package,
const android::String16& type,
const android::String16& name,
bool onlyPublic) {
String16 hashable = String16(name);
hashable += type;
hashable += package;
hashable += (onlyPublic ? TRUE16 : FALSE16);
return hashable;
}
uint32_t ResourceIdCache::lookup(const android::String16& package,
const android::String16& type,
const android::String16& name,
bool onlyPublic) {
const String16 hashedName = makeHashableName(package, type, name, onlyPublic);
const uint32_t hashcode = hash(hashedName);
map<uint32_t, CacheEntry>::iterator item = mIdMap.find(hashcode);
if (item == mIdMap.end()) {
// cache miss
mMisses++;
return 0;
}
// legit match?
if (hashedName == (*item).second.hashedName) {
mHits++;
return (*item).second.id;
}
// collision
mCollisions++;
mIdMap.erase(hashcode);
return 0;
}
// returns the resource ID being stored, for callsite convenience
uint32_t ResourceIdCache::store(const android::String16& package,
const android::String16& type,
const android::String16& name,
bool onlyPublic,
uint32_t resId) {
if (mIdMap.size() < MAX_CACHE_ENTRIES) {
const String16 hashedName = makeHashableName(package, type, name, onlyPublic);
const uint32_t hashcode = hash(hashedName);
mIdMap[hashcode] = CacheEntry(hashedName, resId);
}
return resId;
}
void ResourceIdCache::dump() {
printf("ResourceIdCache dump:\n");
printf("Size: %ld\n", mIdMap.size());
printf("Hits: %ld\n", mHits);
printf("Misses: %ld\n", mMisses);
printf("(Collisions: %ld)\n", mCollisions);
}
}
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