File	Doc	Category	Size	Date	Package
BitLevel.java	API Doc	Android 1.5 API	12473	Wed May 06 22:41:04 BST 2009	java.math

BitLevel

• java.lang.Object

Fields Summary

Constructors Summary
private BitLevel() Just to denote that this class can't be instantiated.

Methods Summary
static int	bitCount(java.math.BigInteger val) see BigInteger#bitCount() // 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;
static int	bitLength(java.math.BigInteger val) see BigInteger#bitLength() // 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;
static java.math.BigInteger	flipBit(java.math.BigInteger val, int n) 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 // 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;
static void	inplaceShiftRight(java.math.BigInteger val, int count) Performs {@code val >>= count} where {@code val} is a positive number. // 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();
static boolean	nonZeroDroppedBits(int numberOfBits, int[] digits) 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 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 java.math.BigInteger	shiftRight(java.math.BigInteger source, int count) see BigInteger#shiftRight(int) // 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;
static boolean	shiftRight(int[] result, int resultLen, int[] source, int intCount, int count) 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) 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;
static boolean	testBit(java.math.BigInteger val, int n) Performs a fast bit testing for positive numbers. The bit to to be tested must be in the range {@code [0, val.bitLength()-1]} // BEGIN android-added val.establishOldRepresentation("BitLevel.testBit"); // END android-added // PRE: 0 <= n < val.bitLength() return ((val.digits[n >> 5] & (1 << (n & 31))) != 0);