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/*
* 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 bit level operations for
* {@link BigInteger}. The operations are:
*
*
Left Shifting
*
Right Shifting
*
Bit clearing
*
Bit setting
*
Bit counting
*
Bit testing
*
Getting of the lowest bit set
*
* All operations are provided in immutable way, and some in both mutable and
* immutable.
*/
class BitLevel {
/** Just to denote that this class can't be instantiated. */
private BitLevel() {}
/** @see BigInteger#bitLength() */
static int bitLength(BigInteger val) {
val.prepareJavaRepresentation();
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) {
val.prepareJavaRepresentation();
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) {
val.prepareJavaRepresentation();
// 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));
}
static void shiftLeftOneBit(int[] result, int[] source, int srcLen) {
int carry = 0;
for (int i = 0; i < srcLen; i++) {
int val = source[i];
result[i] = (val << 1) | carry;
carry = val >>> 31;
}
if(carry != 0) {
result[srcLen] = carry;
}
}
static BigInteger shiftLeftOneBit(BigInteger source) {
source.prepareJavaRepresentation();
int srcLen = source.numberLength;
int resLen = srcLen + 1;
int[] resDigits = new int[resLen];
shiftLeftOneBit(resDigits, source.digits, srcLen);
return new BigInteger(source.sign, resLen, resDigits);
}
/** @see BigInteger#shiftRight(int) */
static BigInteger shiftRight(BigInteger source, int count) {
source.prepareJavaRepresentation();
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]++;
}
}
return new BigInteger(source.sign, resLength, resDigits);
}
/**
* 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.
*/
static BigInteger flipBit(BigInteger val, int n){
val.prepareJavaRepresentation();
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;
}
return new BigInteger(resSign, resLength, resDigits);
}
}
