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77 lines
2.3 KiB
77 lines
2.3 KiB
/*
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* Copyright (C) 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#define LOG_TAG "BitUtils"
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//#define LOG_NDEBUG 0
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#include "BitUtils.h"
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#include <utils/Log.h>
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// Enables debug output for hasKeyInRange
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#define DEBUG_KEY_RANGE 0
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namespace android {
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#if DEBUG_KEY_RANGE
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static const char* bitstrings[16] = {
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"0000", "0001", "0010", "0011",
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"0100", "0101", "0110", "0111",
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"1000", "1001", "1010", "1011",
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"1100", "1101", "1110", "1111",
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};
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#endif
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bool testBitInRange(const uint8_t arr[], size_t start, size_t end) {
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#if DEBUG_KEY_RANGE
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ALOGD("testBitInRange(%d, %d)", start, end);
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#endif
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// Invalid range! This is nonsense; just say no.
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if (end <= start) return false;
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// Find byte array indices. The end is not included in the range, nor is
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// endIndex. Round up for endIndex.
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size_t startIndex = start / 8;
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size_t endIndex = (end + 7) / 8;
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#if DEBUG_KEY_RANGE
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ALOGD("startIndex=%d, endIndex=%d", startIndex, endIndex);
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#endif
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for (size_t i = startIndex; i < endIndex; ++i) {
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uint8_t bits = arr[i];
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uint8_t mask = 0xff;
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#if DEBUG_KEY_RANGE
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ALOGD("block %04d: %s%s", i, bitstrings[bits >> 4], bitstrings[bits & 0x0f]);
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#endif
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if (bits) {
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// Mask off bits before our start bit
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if (i == startIndex) {
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mask &= 0xff << (start % 8);
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}
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// Mask off bits after our end bit
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if (i == endIndex - 1 && (end % 8)) {
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mask &= 0xff >> (8 - (end % 8));
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}
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#if DEBUG_KEY_RANGE
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ALOGD("mask: %s%s", bitstrings[mask >> 4], bitstrings[mask & 0x0f]);
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#endif
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// Test the index against the mask
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if (bits & mask) return true;
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}
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}
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return false;
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}
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} // namespace android
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