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MutableBigInteger.java
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2237 lines (1977 loc) · 70.9 KB
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/*
* Copyright (c) 1999, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
*
*
*
*
*
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*
*
*
*
*
*
*
*/
package java.math;
/**
* A class used to represent multiprecision integers that makes efficient
* use of allocated space by allowing a number to occupy only part of
* an array so that the arrays do not have to be reallocated as often.
* When performing an operation with many iterations the array used to
* hold a number is only reallocated when necessary and does not have to
* be the same size as the number it represents. A mutable number allows
* calculations to occur on the same number without having to create
* a new number for every step of the calculation as occurs with
* BigIntegers.
*
* @see BigInteger
* @author Michael McCloskey
* @author Timothy Buktu
* @since 1.3
*/
import static java.math.BigDecimal.INFLATED;
import static java.math.BigInteger.LONG_MASK;
import java.util.Arrays;
class MutableBigInteger {
/**
* Holds the magnitude of this MutableBigInteger in big endian order.
* The magnitude may start at an offset into the value array, and it may
* end before the length of the value array.
*/
int[] value;
/**
* The number of ints of the value array that are currently used
* to hold the magnitude of this MutableBigInteger. The magnitude starts
* at an offset and offset + intLen may be less than value.length.
*/
int intLen;
/**
* The offset into the value array where the magnitude of this
* MutableBigInteger begins.
*/
int offset = 0;
// Constants
/**
* MutableBigInteger with one element value array with the value 1. Used by
* BigDecimal divideAndRound to increment the quotient. Use this constant
* only when the method is not going to modify this object.
*/
static final MutableBigInteger ONE = new MutableBigInteger(1);
/**
* The minimum {@code intLen} for cancelling powers of two before
* dividing.
* If the number of ints is less than this threshold,
* {@code divideKnuth} does not eliminate common powers of two from
* the dividend and divisor.
*/
static final int KNUTH_POW2_THRESH_LEN = 6;
/**
* The minimum number of trailing zero ints for cancelling powers of two
* before dividing.
* If the dividend and divisor don't share at least this many zero ints
* at the end, {@code divideKnuth} does not eliminate common powers
* of two from the dividend and divisor.
*/
static final int KNUTH_POW2_THRESH_ZEROS = 3;
// Constructors
/**
* The default constructor. An empty MutableBigInteger is created with
* a one word capacity.
*/
MutableBigInteger() {
value = new int[1];
intLen = 0;
}
/**
* Construct a new MutableBigInteger with a magnitude specified by
* the int val.
*/
MutableBigInteger(int val) {
value = new int[1];
intLen = 1;
value[0] = val;
}
/**
* Construct a new MutableBigInteger with the specified value array
* up to the length of the array supplied.
*/
MutableBigInteger(int[] val) {
value = val;
intLen = val.length;
}
/**
* Construct a new MutableBigInteger with a magnitude equal to the
* specified BigInteger.
*/
MutableBigInteger(BigInteger b) {
intLen = b.mag.length;
value = Arrays.copyOf(b.mag, intLen);
}
/**
* Construct a new MutableBigInteger with a magnitude equal to the
* specified MutableBigInteger.
*/
MutableBigInteger(MutableBigInteger val) {
intLen = val.intLen;
value = Arrays.copyOfRange(val.value, val.offset, val.offset + intLen);
}
/**
* Makes this number an {@code n}-int number all of whose bits are ones.
* Used by Burnikel-Ziegler division.
* @param n number of ints in the {@code value} array
* @return a number equal to {@code ((1<<(32*n)))-1}
*/
private void ones(int n) {
if (n > value.length)
value = new int[n];
Arrays.fill(value, -1);
offset = 0;
intLen = n;
}
/**
* Internal helper method to return the magnitude array. The caller is not
* supposed to modify the returned array.
*/
private int[] getMagnitudeArray() {
if (offset > 0 || value.length != intLen)
return Arrays.copyOfRange(value, offset, offset + intLen);
return value;
}
/**
* Convert this MutableBigInteger to a long value. The caller has to make
* sure this MutableBigInteger can be fit into long.
*/
private long toLong() {
assert (intLen <= 2) : "this MutableBigInteger exceeds the range of long";
if (intLen == 0)
return 0;
long d = value[offset] & LONG_MASK;
return (intLen == 2) ? d << 32 | (value[offset + 1] & LONG_MASK) : d;
}
/**
* Convert this MutableBigInteger to a BigInteger object.
*/
BigInteger toBigInteger(int sign) {
if (intLen == 0 || sign == 0)
return BigInteger.ZERO;
return new BigInteger(getMagnitudeArray(), sign);
}
/**
* Converts this number to a nonnegative {@code BigInteger}.
*/
BigInteger toBigInteger() {
normalize();
return toBigInteger(isZero() ? 0 : 1);
}
/**
* Convert this MutableBigInteger to BigDecimal object with the specified sign
* and scale.
*/
BigDecimal toBigDecimal(int sign, int scale) {
if (intLen == 0 || sign == 0)
return BigDecimal.zeroValueOf(scale);
int[] mag = getMagnitudeArray();
int len = mag.length;
int d = mag[0];
// If this MutableBigInteger can't be fit into long, we need to
// make a BigInteger object for the resultant BigDecimal object.
if (len > 2 || (d < 0 && len == 2))
return new BigDecimal(new BigInteger(mag, sign), INFLATED, scale, 0);
long v = (len == 2) ?
((mag[1] & LONG_MASK) | (d & LONG_MASK) << 32) :
d & LONG_MASK;
return BigDecimal.valueOf(sign == -1 ? -v : v, scale);
}
/**
* This is for internal use in converting from a MutableBigInteger
* object into a long value given a specified sign.
* returns INFLATED if value is not fit into long
*/
long toCompactValue(int sign) {
if (intLen == 0 || sign == 0)
return 0L;
int[] mag = getMagnitudeArray();
int len = mag.length;
int d = mag[0];
// If this MutableBigInteger can not be fitted into long, we need to
// make a BigInteger object for the resultant BigDecimal object.
if (len > 2 || (d < 0 && len == 2))
return INFLATED;
long v = (len == 2) ?
((mag[1] & LONG_MASK) | (d & LONG_MASK) << 32) :
d & LONG_MASK;
return sign == -1 ? -v : v;
}
/**
* Clear out a MutableBigInteger for reuse.
*/
void clear() {
offset = intLen = 0;
for (int index=0, n=value.length; index < n; index++)
value[index] = 0;
}
/**
* Set a MutableBigInteger to zero, removing its offset.
*/
void reset() {
offset = intLen = 0;
}
/**
* Compare the magnitude of two MutableBigIntegers. Returns -1, 0 or 1
* as this MutableBigInteger is numerically less than, equal to, or
* greater than <tt>b</tt>.
*/
final int compare(MutableBigInteger b) {
int blen = b.intLen;
if (intLen < blen)
return -1;
if (intLen > blen)
return 1;
// Add Integer.MIN_VALUE to make the comparison act as unsigned integer
// comparison.
int[] bval = b.value;
for (int i = offset, j = b.offset; i < intLen + offset; i++, j++) {
int b1 = value[i] + 0x80000000;
int b2 = bval[j] + 0x80000000;
if (b1 < b2)
return -1;
if (b1 > b2)
return 1;
}
return 0;
}
/**
* Returns a value equal to what {@code b.leftShift(32*ints); return compare(b);}
* would return, but doesn't change the value of {@code b}.
*/
private int compareShifted(MutableBigInteger b, int ints) {
int blen = b.intLen;
int alen = intLen - ints;
if (alen < blen)
return -1;
if (alen > blen)
return 1;
// Add Integer.MIN_VALUE to make the comparison act as unsigned integer
// comparison.
int[] bval = b.value;
for (int i = offset, j = b.offset; i < alen + offset; i++, j++) {
int b1 = value[i] + 0x80000000;
int b2 = bval[j] + 0x80000000;
if (b1 < b2)
return -1;
if (b1 > b2)
return 1;
}
return 0;
}
/**
* Compare this against half of a MutableBigInteger object (Needed for
* remainder tests).
* Assumes no leading unnecessary zeros, which holds for results
* from divide().
*/
final int compareHalf(MutableBigInteger b) {
int blen = b.intLen;
int len = intLen;
if (len <= 0)
return blen <= 0 ? 0 : -1;
if (len > blen)
return 1;
if (len < blen - 1)
return -1;
int[] bval = b.value;
int bstart = 0;
int carry = 0;
// Only 2 cases left:len == blen or len == blen - 1
if (len != blen) { // len == blen - 1
if (bval[bstart] == 1) {
++bstart;
carry = 0x80000000;
} else
return -1;
}
// compare values with right-shifted values of b,
// carrying shifted-out bits across words
int[] val = value;
for (int i = offset, j = bstart; i < len + offset;) {
int bv = bval[j++];
long hb = ((bv >>> 1) + carry) & LONG_MASK;
long v = val[i++] & LONG_MASK;
if (v != hb)
return v < hb ? -1 : 1;
carry = (bv & 1) << 31; // carray will be either 0x80000000 or 0
}
return carry == 0 ? 0 : -1;
}
/**
* Return the index of the lowest set bit in this MutableBigInteger. If the
* magnitude of this MutableBigInteger is zero, -1 is returned.
*/
private final int getLowestSetBit() {
if (intLen == 0)
return -1;
int j, b;
for (j=intLen-1; (j > 0) && (value[j+offset] == 0); j--)
;
b = value[j+offset];
if (b == 0)
return -1;
return ((intLen-1-j)<<5) + Integer.numberOfTrailingZeros(b);
}
/**
* Return the int in use in this MutableBigInteger at the specified
* index. This method is not used because it is not inlined on all
* platforms.
*/
private final int getInt(int index) {
return value[offset+index];
}
/**
* Return a long which is equal to the unsigned value of the int in
* use in this MutableBigInteger at the specified index. This method is
* not used because it is not inlined on all platforms.
*/
private final long getLong(int index) {
return value[offset+index] & LONG_MASK;
}
/**
* Ensure that the MutableBigInteger is in normal form, specifically
* making sure that there are no leading zeros, and that if the
* magnitude is zero, then intLen is zero.
*/
final void normalize() {
if (intLen == 0) {
offset = 0;
return;
}
int index = offset;
if (value[index] != 0)
return;
int indexBound = index+intLen;
do {
index++;
} while(index < indexBound && value[index] == 0);
int numZeros = index - offset;
intLen -= numZeros;
offset = (intLen == 0 ? 0 : offset+numZeros);
}
/**
* If this MutableBigInteger cannot hold len words, increase the size
* of the value array to len words.
*/
private final void ensureCapacity(int len) {
if (value.length < len) {
value = new int[len];
offset = 0;
intLen = len;
}
}
/**
* Convert this MutableBigInteger into an int array with no leading
* zeros, of a length that is equal to this MutableBigInteger's intLen.
*/
int[] toIntArray() {
int[] result = new int[intLen];
for(int i=0; i < intLen; i++)
result[i] = value[offset+i];
return result;
}
/**
* Sets the int at index+offset in this MutableBigInteger to val.
* This does not get inlined on all platforms so it is not used
* as often as originally intended.
*/
void setInt(int index, int val) {
value[offset + index] = val;
}
/**
* Sets this MutableBigInteger's value array to the specified array.
* The intLen is set to the specified length.
*/
void setValue(int[] val, int length) {
value = val;
intLen = length;
offset = 0;
}
/**
* Sets this MutableBigInteger's value array to a copy of the specified
* array. The intLen is set to the length of the new array.
*/
void copyValue(MutableBigInteger src) {
int len = src.intLen;
if (value.length < len)
value = new int[len];
System.arraycopy(src.value, src.offset, value, 0, len);
intLen = len;
offset = 0;
}
/**
* Sets this MutableBigInteger's value array to a copy of the specified
* array. The intLen is set to the length of the specified array.
*/
void copyValue(int[] val) {
int len = val.length;
if (value.length < len)
value = new int[len];
System.arraycopy(val, 0, value, 0, len);
intLen = len;
offset = 0;
}
/**
* Returns true iff this MutableBigInteger has a value of one.
*/
boolean isOne() {
return (intLen == 1) && (value[offset] == 1);
}
/**
* Returns true iff this MutableBigInteger has a value of zero.
*/
boolean isZero() {
return (intLen == 0);
}
/**
* Returns true iff this MutableBigInteger is even.
*/
boolean isEven() {
return (intLen == 0) || ((value[offset + intLen - 1] & 1) == 0);
}
/**
* Returns true iff this MutableBigInteger is odd.
*/
boolean isOdd() {
return isZero() ? false : ((value[offset + intLen - 1] & 1) == 1);
}
/**
* Returns true iff this MutableBigInteger is in normal form. A
* MutableBigInteger is in normal form if it has no leading zeros
* after the offset, and intLen + offset <= value.length.
*/
boolean isNormal() {
if (intLen + offset > value.length)
return false;
if (intLen == 0)
return true;
return (value[offset] != 0);
}
/**
* Returns a String representation of this MutableBigInteger in radix 10.
*/
public String toString() {
BigInteger b = toBigInteger(1);
return b.toString();
}
/**
* Like {@link #rightShift(int)} but {@code n} can be greater than the length of the number.
*/
void safeRightShift(int n) {
if (n/32 >= intLen) {
reset();
} else {
rightShift(n);
}
}
/**
* Right shift this MutableBigInteger n bits. The MutableBigInteger is left
* in normal form.
*/
void rightShift(int n) {
if (intLen == 0)
return;
int nInts = n >>> 5;
int nBits = n & 0x1F;
this.intLen -= nInts;
if (nBits == 0)
return;
int bitsInHighWord = BigInteger.bitLengthForInt(value[offset]);
if (nBits >= bitsInHighWord) {
this.primitiveLeftShift(32 - nBits);
this.intLen--;
} else {
primitiveRightShift(nBits);
}
}
/**
* Like {@link #leftShift(int)} but {@code n} can be zero.
*/
void safeLeftShift(int n) {
if (n > 0) {
leftShift(n);
}
}
/**
* Left shift this MutableBigInteger n bits.
*/
void leftShift(int n) {
/*
* If there is enough storage space in this MutableBigInteger already
* the available space will be used. Space to the right of the used
* ints in the value array is faster to utilize, so the extra space
* will be taken from the right if possible.
*/
if (intLen == 0)
return;
int nInts = n >>> 5;
int nBits = n&0x1F;
int bitsInHighWord = BigInteger.bitLengthForInt(value[offset]);
// If shift can be done without moving words, do so
if (n <= (32-bitsInHighWord)) {
primitiveLeftShift(nBits);
return;
}
int newLen = intLen + nInts +1;
if (nBits <= (32-bitsInHighWord))
newLen--;
if (value.length < newLen) {
// The array must grow
int[] result = new int[newLen];
for (int i=0; i < intLen; i++)
result[i] = value[offset+i];
setValue(result, newLen);
} else if (value.length - offset >= newLen) {
// Use space on right
for(int i=0; i < newLen - intLen; i++)
value[offset+intLen+i] = 0;
} else {
// Must use space on left
for (int i=0; i < intLen; i++)
value[i] = value[offset+i];
for (int i=intLen; i < newLen; i++)
value[i] = 0;
offset = 0;
}
intLen = newLen;
if (nBits == 0)
return;
if (nBits <= (32-bitsInHighWord))
primitiveLeftShift(nBits);
else
primitiveRightShift(32 -nBits);
}
/**
* A primitive used for division. This method adds in one multiple of the
* divisor a back to the dividend result at a specified offset. It is used
* when qhat was estimated too large, and must be adjusted.
*/
private int divadd(int[] a, int[] result, int offset) {
long carry = 0;
for (int j=a.length-1; j >= 0; j--) {
long sum = (a[j] & LONG_MASK) +
(result[j+offset] & LONG_MASK) + carry;
result[j+offset] = (int)sum;
carry = sum >>> 32;
}
return (int)carry;
}
/**
* This method is used for division. It multiplies an n word input a by one
* word input x, and subtracts the n word product from q. This is needed
* when subtracting qhat*divisor from dividend.
*/
private int mulsub(int[] q, int[] a, int x, int len, int offset) {
long xLong = x & LONG_MASK;
long carry = 0;
offset += len;
for (int j=len-1; j >= 0; j--) {
long product = (a[j] & LONG_MASK) * xLong + carry;
long difference = q[offset] - product;
q[offset--] = (int)difference;
carry = (product >>> 32)
+ (((difference & LONG_MASK) >
(((~(int)product) & LONG_MASK))) ? 1:0);
}
return (int)carry;
}
/**
* The method is the same as mulsun, except the fact that q array is not
* updated, the only result of the method is borrow flag.
*/
private int mulsubBorrow(int[] q, int[] a, int x, int len, int offset) {
long xLong = x & LONG_MASK;
long carry = 0;
offset += len;
for (int j=len-1; j >= 0; j--) {
long product = (a[j] & LONG_MASK) * xLong + carry;
long difference = q[offset--] - product;
carry = (product >>> 32)
+ (((difference & LONG_MASK) >
(((~(int)product) & LONG_MASK))) ? 1:0);
}
return (int)carry;
}
/**
* Right shift this MutableBigInteger n bits, where n is
* less than 32.
* Assumes that intLen > 0, n > 0 for speed
*/
private final void primitiveRightShift(int n) {
int[] val = value;
int n2 = 32 - n;
for (int i=offset+intLen-1, c=val[i]; i > offset; i--) {
int b = c;
c = val[i-1];
val[i] = (c << n2) | (b >>> n);
}
val[offset] >>>= n;
}
/**
* Left shift this MutableBigInteger n bits, where n is
* less than 32.
* Assumes that intLen > 0, n > 0 for speed
*/
private final void primitiveLeftShift(int n) {
int[] val = value;
int n2 = 32 - n;
for (int i=offset, c=val[i], m=i+intLen-1; i < m; i++) {
int b = c;
c = val[i+1];
val[i] = (b << n) | (c >>> n2);
}
val[offset+intLen-1] <<= n;
}
/**
* Returns a {@code BigInteger} equal to the {@code n}
* low ints of this number.
*/
private BigInteger getLower(int n) {
if (isZero()) {
return BigInteger.ZERO;
} else if (intLen < n) {
return toBigInteger(1);
} else {
// strip zeros
int len = n;
while (len > 0 && value[offset+intLen-len] == 0)
len--;
int sign = len > 0 ? 1 : 0;
return new BigInteger(Arrays.copyOfRange(value, offset+intLen-len, offset+intLen), sign);
}
}
/**
* Discards all ints whose index is greater than {@code n}.
*/
private void keepLower(int n) {
if (intLen >= n) {
offset += intLen - n;
intLen = n;
}
}
/**
* Adds the contents of two MutableBigInteger objects.The result
* is placed within this MutableBigInteger.
* The contents of the addend are not changed.
*/
void add(MutableBigInteger addend) {
int x = intLen;
int y = addend.intLen;
int resultLen = (intLen > addend.intLen ? intLen : addend.intLen);
int[] result = (value.length < resultLen ? new int[resultLen] : value);
int rstart = result.length-1;
long sum;
long carry = 0;
// Add common parts of both numbers
while(x > 0 && y > 0) {
x--; y--;
sum = (value[x+offset] & LONG_MASK) +
(addend.value[y+addend.offset] & LONG_MASK) + carry;
result[rstart--] = (int)sum;
carry = sum >>> 32;
}
// Add remainder of the longer number
while(x > 0) {
x--;
if (carry == 0 && result == value && rstart == (x + offset))
return;
sum = (value[x+offset] & LONG_MASK) + carry;
result[rstart--] = (int)sum;
carry = sum >>> 32;
}
while(y > 0) {
y--;
sum = (addend.value[y+addend.offset] & LONG_MASK) + carry;
result[rstart--] = (int)sum;
carry = sum >>> 32;
}
if (carry > 0) { // Result must grow in length
resultLen++;
if (result.length < resultLen) {
int temp[] = new int[resultLen];
// Result one word longer from carry-out; copy low-order
// bits into new result.
System.arraycopy(result, 0, temp, 1, result.length);
temp[0] = 1;
result = temp;
} else {
result[rstart--] = 1;
}
}
value = result;
intLen = resultLen;
offset = result.length - resultLen;
}
/**
* Adds the value of {@code addend} shifted {@code n} ints to the left.
* Has the same effect as {@code addend.leftShift(32*ints); add(addend);}
* but doesn't change the value of {@code addend}.
*/
void addShifted(MutableBigInteger addend, int n) {
if (addend.isZero()) {
return;
}
int x = intLen;
int y = addend.intLen + n;
int resultLen = (intLen > y ? intLen : y);
int[] result = (value.length < resultLen ? new int[resultLen] : value);
int rstart = result.length-1;
long sum;
long carry = 0;
// Add common parts of both numbers
while (x > 0 && y > 0) {
x--; y--;
int bval = y+addend.offset < addend.value.length ? addend.value[y+addend.offset] : 0;
sum = (value[x+offset] & LONG_MASK) +
(bval & LONG_MASK) + carry;
result[rstart--] = (int)sum;
carry = sum >>> 32;
}
// Add remainder of the longer number
while (x > 0) {
x--;
if (carry == 0 && result == value && rstart == (x + offset)) {
return;
}
sum = (value[x+offset] & LONG_MASK) + carry;
result[rstart--] = (int)sum;
carry = sum >>> 32;
}
while (y > 0) {
y--;
int bval = y+addend.offset < addend.value.length ? addend.value[y+addend.offset] : 0;
sum = (bval & LONG_MASK) + carry;
result[rstart--] = (int)sum;
carry = sum >>> 32;
}
if (carry > 0) { // Result must grow in length
resultLen++;
if (result.length < resultLen) {
int temp[] = new int[resultLen];
// Result one word longer from carry-out; copy low-order
// bits into new result.
System.arraycopy(result, 0, temp, 1, result.length);
temp[0] = 1;
result = temp;
} else {
result[rstart--] = 1;
}
}
value = result;
intLen = resultLen;
offset = result.length - resultLen;
}
/**
* Like {@link #addShifted(MutableBigInteger, int)} but {@code this.intLen} must
* not be greater than {@code n}. In other words, concatenates {@code this}
* and {@code addend}.
*/
void addDisjoint(MutableBigInteger addend, int n) {
if (addend.isZero())
return;
int x = intLen;
int y = addend.intLen + n;
int resultLen = (intLen > y ? intLen : y);
int[] result;
if (value.length < resultLen)
result = new int[resultLen];
else {
result = value;
Arrays.fill(value, offset+intLen, value.length, 0);
}
int rstart = result.length-1;
// copy from this if needed
System.arraycopy(value, offset, result, rstart+1-x, x);
y -= x;
rstart -= x;
int len = Math.min(y, addend.value.length-addend.offset);
System.arraycopy(addend.value, addend.offset, result, rstart+1-y, len);
// zero the gap
for (int i=rstart+1-y+len; i < rstart+1; i++)
result[i] = 0;
value = result;
intLen = resultLen;
offset = result.length - resultLen;
}
/**
* Adds the low {@code n} ints of {@code addend}.
*/
void addLower(MutableBigInteger addend, int n) {
MutableBigInteger a = new MutableBigInteger(addend);
if (a.offset + a.intLen >= n) {
a.offset = a.offset + a.intLen - n;
a.intLen = n;
}
a.normalize();
add(a);
}
/**
* Subtracts the smaller of this and b from the larger and places the
* result into this MutableBigInteger.
*/
int subtract(MutableBigInteger b) {
MutableBigInteger a = this;
int[] result = value;
int sign = a.compare(b);
if (sign == 0) {
reset();
return 0;
}
if (sign < 0) {
MutableBigInteger tmp = a;
a = b;
b = tmp;
}
int resultLen = a.intLen;
if (result.length < resultLen)
result = new int[resultLen];
long diff = 0;
int x = a.intLen;
int y = b.intLen;
int rstart = result.length - 1;
// Subtract common parts of both numbers
while (y > 0) {
x--; y--;
diff = (a.value[x+a.offset] & LONG_MASK) -
(b.value[y+b.offset] & LONG_MASK) - ((int)-(diff>>32));
result[rstart--] = (int)diff;
}
// Subtract remainder of longer number
while (x > 0) {
x--;
diff = (a.value[x+a.offset] & LONG_MASK) - ((int)-(diff>>32));
result[rstart--] = (int)diff;
}
value = result;
intLen = resultLen;
offset = value.length - resultLen;
normalize();
return sign;
}
/**
* Subtracts the smaller of a and b from the larger and places the result
* into the larger. Returns 1 if the answer is in a, -1 if in b, 0 if no
* operation was performed.
*/
private int difference(MutableBigInteger b) {
MutableBigInteger a = this;
int sign = a.compare(b);
if (sign == 0)
return 0;
if (sign < 0) {
MutableBigInteger tmp = a;
a = b;
b = tmp;
}
long diff = 0;
int x = a.intLen;
int y = b.intLen;
// Subtract common parts of both numbers
while (y > 0) {
x--; y--;
diff = (a.value[a.offset+ x] & LONG_MASK) -
(b.value[b.offset+ y] & LONG_MASK) - ((int)-(diff>>32));
a.value[a.offset+x] = (int)diff;
}
// Subtract remainder of longer number
while (x > 0) {
x--;
diff = (a.value[a.offset+ x] & LONG_MASK) - ((int)-(diff>>32));
a.value[a.offset+x] = (int)diff;
}
a.normalize();
return sign;
}
/**
* Multiply the contents of two MutableBigInteger objects. The result is
* placed into MutableBigInteger z. The contents of y are not changed.