/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
package java.math;
/**
* Static library that provides all the <b>bit level</b> operations for
* {@link BigInteger}. The operations are:
* <ul type="circle">
* <li>Left Shifting</li>
* <li>Right Shifting</li>
* <li>Bit clearing</li>
* <li>Bit setting</li>
* <li>Bit counting</li>
* <li>Bit testing</li>
* <li>Getting of the lowest bit set</li>
* </ul>
* All operations are provided in immutable way, and some in both mutable and
* immutable.
*
* @author Intel Middleware Product Division
* @author Instituto Tecnologico de Cordoba
*/
class BitLevel {
/** Just to denote that this class can't be instantiated. */
private BitLevel() {}
/** @see BigInteger#bitLength() */
static int bitLength(BigInteger val) {
// BEGIN android-added
val.establishOldRepresentation("BitLevel.bitLength");
// END android-added
if (val.sign == 0) {
return 0;
}
int bLength = (val.numberLength << 5);
int highDigit = val.digits[val.numberLength - 1];
if (val.sign < 0) {
int i = val.getFirstNonzeroDigit();
// We reduce the problem to the positive case.
if (i == val.numberLength - 1) {
highDigit--;
}
}
// Subtracting all sign bits
bLength -= Integer.numberOfLeadingZeros(highDigit);
return bLength;
}
/** @see BigInteger#bitCount() */
static int bitCount(BigInteger val) {
// BEGIN android-added
val.establishOldRepresentation("BitLevel.bitCount");
// END android-added
int bCount = 0;
if (val.sign == 0) {
return 0;
}
int i = val.getFirstNonzeroDigit();;
if (val.sign > 0) {
for ( ; i < val.numberLength; i++) {
bCount += Integer.bitCount(val.digits[i]);
}
} else {// (sign < 0)
// this digit absorbs the carry
bCount += Integer.bitCount(-val.digits[i]);
for (i++; i < val.numberLength; i++) {
bCount += Integer.bitCount(~val.digits[i]);
}
// We take the complement sum:
bCount = (val.numberLength << 5) - bCount;
}
return bCount;
}
/**
* Performs a fast bit testing for positive numbers. The bit to to be tested
* must be in the range {@code [0, val.bitLength()-1]}
*/
static boolean testBit(BigInteger val, int n) {
// BEGIN android-added
val.establishOldRepresentation("BitLevel.testBit");
// END android-added
// PRE: 0 <= n < val.bitLength()
return ((val.digits[n >> 5] & (1 << (n & 31))) != 0);
}
/**
* Check if there are 1s in the lowest bits of this BigInteger
*
* @param numberOfBits the number of the lowest bits to check
* @return false if all bits are 0s, true otherwise
*/
static boolean nonZeroDroppedBits(int numberOfBits, int digits[]) {
int intCount = numberOfBits >> 5;
int bitCount = numberOfBits & 31;
int i;
for (i = 0; (i < intCount) && (digits[i] == 0); i++) {
;
}
return ((i != intCount) || (digits[i] << (32 - bitCount) != 0));
}
// BEGIN android-removed
// /** @see BigInteger#shiftLeft(int) */
// static BigInteger shiftLeft(BigInteger source, int count) {
// int intCount = count >> 5;
// count &= 31; // %= 32
// int resLength = source.numberLength + intCount
// + ( ( count == 0 ) ? 0 : 1 );
// int resDigits[] = new int[resLength];
//
// shiftLeft(resDigits, source.digits, intCount, count);
// BigInteger result = new BigInteger(source.sign, resLength, resDigits);
// result.cutOffLeadingZeroes();
// return result;
// }
//
// /**
// * Performs {@code val <<= count}.
// */
// // val should have enough place (and one digit more)
// static void inplaceShiftLeft(BigInteger val, int count) {
// int intCount = count >> 5; // count of integers
// val.numberLength += intCount
// + ( Integer
// .numberOfLeadingZeros(val.digits[val.numberLength - 1])
// - ( count & 31 ) >= 0 ? 0 : 1 );
// shiftLeft(val.digits, val.digits, intCount, count & 31);
// val.cutOffLeadingZeroes();
// val.unCache();
// }
//
// /**
// * Abstractly shifts left an array of integers in little endian (i.e. shift
// * it right). Total shift distance in bits is intCount * 32 + count
// *
// * @param result the destination array
// * @param source the source array
// * @param intCount the shift distance in integers
// * @param count an additional shift distance in bits
// */
// static void shiftLeft(int result[], int source[], int intCount, int count) {
// if (count == 0) {
// System.arraycopy(source, 0, result, intCount, result.length
// - intCount);
// } else {
// int rightShiftCount = 32 - count;
//
// result[result.length - 1] = 0;
// for (int i = result.length - 1; i > intCount; i--) {
// result[i] |= source[i - intCount - 1] >>> rightShiftCount;
// result[i - 1] = source[i - intCount - 1] << count;
// }
// }
//
// for (int i = 0; i < intCount; i++) {
// result[i] = 0;
// }
// }
// END android-removed
/** @see BigInteger#shiftRight(int) */
static BigInteger shiftRight(BigInteger source, int count) {
// BEGIN android-added
source.establishOldRepresentation("BitLevel.shiftRight");
// END android-added
int intCount = count >> 5; // count of integers
count &= 31; // count of remaining bits
if (intCount >= source.numberLength) {
return ((source.sign < 0) ? BigInteger.MINUS_ONE : BigInteger.ZERO);
}
int i;
int resLength = source.numberLength - intCount;
int resDigits[] = new int[resLength + 1];
shiftRight(resDigits, resLength, source.digits, intCount, count);
if (source.sign < 0) {
// Checking if the dropped bits are zeros (the remainder equals to
// 0)
for (i = 0; (i < intCount) && (source.digits[i] == 0); i++) {
;
}
// If the remainder is not zero, add 1 to the result
if ((i < intCount)
|| ((count > 0) && ((source.digits[i] << (32 - count)) != 0))) {
for (i = 0; (i < resLength) && (resDigits[i] == -1); i++) {
resDigits[i] = 0;
}
if (i == resLength) {
resLength++;
}
resDigits[i]++;
}
}
BigInteger result = new BigInteger(source.sign, resLength, resDigits);
result.cutOffLeadingZeroes();
return result;
}
/**
* Performs {@code val >>= count} where {@code val} is a positive number.
*/
static void inplaceShiftRight(BigInteger val, int count) {
// BEGIN android-added
val.establishOldRepresentation("BitLevel.inplaceShiftRight");
// END android-added
int sign = val.signum();
if (count == 0 || val.signum() == 0)
return;
int intCount = count >> 5; // count of integers
val.numberLength -= intCount;
if (!shiftRight(val.digits, val.numberLength, val.digits, intCount,
count & 31)
&& sign < 0) {
// remainder not zero: add one to the result
int i;
for (i = 0; ( i < val.numberLength ) && ( val.digits[i] == -1 ); i++) {
val.digits[i] = 0;
}
if (i == val.numberLength) {
val.numberLength++;
}
val.digits[i]++;
}
val.cutOffLeadingZeroes();
val.unCache();
}
/**
* Shifts right an array of integers. Total shift distance in bits is
* intCount * 32 + count.
*
* @param result
* the destination array
* @param resultLen
* the destination array's length
* @param source
* the source array
* @param intCount
* the number of elements to be shifted
* @param count
* the number of bits to be shifted
* @return dropped bit's are all zero (i.e. remaider is zero)
*/
static boolean shiftRight(int result[], int resultLen, int source[],
int intCount, int count) {
int i;
boolean allZero = true;
for (i = 0; i < intCount; i++)
allZero &= source[i] == 0;
if (count == 0) {
System.arraycopy(source, intCount, result, 0, resultLen);
i = resultLen;
} else {
int leftShiftCount = 32 - count;
allZero &= ( source[i] << leftShiftCount ) == 0;
for (i = 0; i < resultLen - 1; i++) {
result[i] = ( source[i + intCount] >>> count )
| ( source[i + intCount + 1] << leftShiftCount );
}
result[i] = ( source[i + intCount] >>> count );
i++;
}
return allZero;
}
/**
* Performs a flipBit on the BigInteger, returning a BigInteger with the the
* specified bit flipped.
* @param intCount: the index of the element of the digits array where the operation will be performed
* @param bitNumber: the bit's position in the intCount element
*/
static BigInteger flipBit(BigInteger val, int n){
// BEGIN android-added
val.establishOldRepresentation("BitLevel.flipBit");
// END android-added
int resSign = (val.sign == 0) ? 1 : val.sign;
int intCount = n >> 5;
int bitN = n & 31;
int resLength = Math.max(intCount + 1, val.numberLength) + 1;
int resDigits[] = new int[resLength];
int i;
int bitNumber = 1 << bitN;
System.arraycopy(val.digits, 0, resDigits, 0, val.numberLength);
if (val.sign < 0) {
if (intCount >= val.numberLength) {
resDigits[intCount] = bitNumber;
} else {
//val.sign<0 y intCount < val.numberLength
int firstNonZeroDigit = val.getFirstNonzeroDigit();
if (intCount > firstNonZeroDigit) {
resDigits[intCount] ^= bitNumber;
} else if (intCount < firstNonZeroDigit) {
resDigits[intCount] = -bitNumber;
for (i=intCount + 1; i < firstNonZeroDigit; i++) {
resDigits[i]=-1;
}
resDigits[i] = resDigits[i]--;
} else {
i = intCount;
resDigits[i] = -((-resDigits[intCount]) ^ bitNumber);
if (resDigits[i] == 0) {
for (i++; resDigits[i] == -1 ; i++) {
resDigits[i] = 0;
}
resDigits[i]++;
}
}
}
} else {//case where val is positive
resDigits[intCount] ^= bitNumber;
}
BigInteger result = new BigInteger(resSign, resLength, resDigits);
result.cutOffLeadingZeroes();
return result;
}
}
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