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// Copyright (C) 2014 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "emugl/common/id_to_object_map.h"
#include <stdlib.h>
namespace emugl {
namespace {
typedef IdToObjectMapBase::KeyType KeyType;
enum {
kMinShift = 3,
kMaxShift = 31,
kMinCapacity = (1 << kMinShift),
kLoadScale = 1024,
kMinLoad = kLoadScale/4, // 25% minimum load.
kMaxLoad = kLoadScale*3/4, // 75% maximum load.
kInvalidKey = IdToObjectMapBase::kMaxId + 1U,
kTombstone = IdToObjectMapBase::kMaxId + 2U,
};
// Return a number that indicates if the current |capacity| is appropriate
// to hold |size| items in our map.
// -1 -> the capacity is too small and needs to be increased.
// 0 -> the capacity is ok.
// +1 -> the capacity is too large and needs to be decreased.
int capacityCompare(size_t shift, size_t size) {
size_t capacity = 1U << shift;
// Essentially, one can rewrite:
// load < minLoad
// as:
// size / capacity < minLoad
// capacity * minLoad > size
if (capacity * kMinLoad > size * kLoadScale)
return +1;
// Similarly, one can rewrite:
// load > maxLoad
// as:
// size / capacity > maxLoad
// capacity * maxLoad < size
if (capacity * kMaxLoad < size * kLoadScale)
return -1;
return 0;
}
size_t probeKeys(const KeyType* keys, size_t shift, KeyType key) {
static const int kPrimes[] = {
1, /* For 1 << 0 */
2,
3,
7,
13,
31,
61,
127,
251,
509,
1021,
2039,
4093,
8191,
16381,
32749,
65521, /* For 1 << 16 */
131071,
262139,
524287,
1048573,
2097143,
4194301,
8388593,
16777213,
33554393,
67108859,
134217689,
268435399,
536870909,
1073741789,
2147483647 /* For 1 << 31 */
};
size_t slot = key % kPrimes[shift];
size_t step = 0;
for (;;) {
KeyType k = keys[slot];
if (k == kInvalidKey || k == kTombstone || k == key)
return slot;
step += 1;
slot = (slot + step) & (1U << shift);
}
}
} // namespace
IdToObjectMapBase::IdToObjectMapBase() :
mCount(0), mShift(kMinShift) {
size_t capacity = 1U << mShift;
mKeys = static_cast<KeyType*>(::calloc(sizeof(mKeys[0]), capacity));
mValues = static_cast<void**>(::calloc(sizeof(mValues[0]), capacity));
for (size_t n = 0; n < capacity; ++n) {
mKeys[n] = kInvalidKey;
}
}
IdToObjectMapBase::~IdToObjectMapBase() {
mShift = 0;
mCount = 0;
::free(mKeys);
::free(mValues);
}
bool IdToObjectMapBase::contains(KeyType key) const {
size_t slot = probeKeys(mKeys, mShift, key);
switch (mKeys[slot]) {
case kInvalidKey:
case kTombstone:
return false;
default:
;
}
return true;
}
bool IdToObjectMapBase::find(KeyType key, void** value) const {
size_t slot = probeKeys(mKeys, mShift, key);
if (!isValidKey(mKeys[slot])) {
*value = NULL;
return false;
}
*value = mValues[slot];
return true;
}
void* IdToObjectMapBase::set(KeyType key, void* value) {
if (!value)
return remove(key);
size_t slot = probeKeys(mKeys, mShift, key);
void* result;
if (isValidKey(mKeys[slot])) {
result = mValues[slot];
mValues[slot] = value;
} else {
mKeys[slot] = key;
mValues[slot] = value;
result = NULL;
mCount++;
resize(mCount);
}
return result;
}
void* IdToObjectMapBase::remove(KeyType key) {
size_t slot = probeKeys(mKeys, mShift, key);
if (!isValidKey(mKeys[slot]))
return NULL;
void* result = mValues[slot];
mValues[slot] = NULL;
mKeys[slot] = kTombstone;
mCount--;
return result;
}
void IdToObjectMapBase::resize(size_t newSize) {
int ret = capacityCompare(mShift, newSize);
if (!ret)
return;
size_t oldCapacity = 1U << mShift;
size_t newShift = mShift;
if (ret < 0) {
// Capacity is too small and must be increased.
do {
if (newShift == kMaxShift)
break;
++newShift;
} while (capacityCompare(newShift, newSize) < 0);
} else {
// Capacity is too large and must be decreased.
do {
if (newShift == kMinShift)
break;
newShift--;
} while (capacityCompare(newShift, newSize) > 0);
}
if (newShift == mShift)
return;
// Allocate new arrays.
size_t newCapacity = 1U << newShift;
KeyType* newKeys = static_cast<KeyType*>(
::calloc(sizeof(newKeys[0]), newCapacity));
void** newValues = static_cast<void**>(
::calloc(sizeof(newValues[0]), newCapacity));
for (size_t n = 0; n < newCapacity; ++n)
newKeys[n] = kInvalidKey;
// Copy old entries into new arrays.
for (size_t n = 0; n < oldCapacity; ++n) {
KeyType key = mKeys[n];
if (isValidKey(key)) {
size_t newSlot = probeKeys(newKeys, newShift, key);
newKeys[newSlot] = key;
newValues[newSlot] = mValues[n];
}
}
// Swap arrays, and get rid of old ones.
::free(mKeys);
::free(mValues);
mKeys = newKeys;
mValues = newValues;
mShift = newShift;
}
} // namespace emugl
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