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25 
26 package java.math;
27 
28 /**
29  * A class used to represent multiprecision integers that makes efficient
30  * use of allocated space by allowing a number to occupy only part of
31  * an array so that the arrays do not have to be reallocated as often.
32  * When performing an operation with many iterations the array used to
33  * hold a number is only increased when necessary and does not have to
34  * be the same size as the number it represents. A mutable number allows
35  * calculations to occur on the same number without having to create
36  * a new number for every step of the calculation as occurs with
37  * BigIntegers.
38  *
39  * Note that SignedMutableBigIntegers only support signed addition and
40  * subtraction. All other operations occur as with MutableBigIntegers.
41  *
42  * @see     BigInteger
43  * @author  Michael McCloskey
44  * @since   1.3
45  */
46 
47 class SignedMutableBigInteger extends MutableBigInteger {
48 
49    /**
50      * The sign of this MutableBigInteger.
51      */
52     int sign = 1;
53 
54     // Constructors
55 
56     /**
57      * The default constructor. An empty MutableBigInteger is created with
58      * a one word capacity.
59      */
SignedMutableBigInteger()60     SignedMutableBigInteger() {
61         super();
62     }
63 
64     /**
65      * Construct a new MutableBigInteger with a magnitude specified by
66      * the int val.
67      */
SignedMutableBigInteger(int val)68     SignedMutableBigInteger(int val) {
69         super(val);
70     }
71 
72     /**
73      * Construct a new MutableBigInteger with a magnitude equal to the
74      * specified MutableBigInteger.
75      */
SignedMutableBigInteger(MutableBigInteger val)76     SignedMutableBigInteger(MutableBigInteger val) {
77         super(val);
78     }
79 
80    // Arithmetic Operations
81 
82    /**
83      * Signed addition built upon unsigned add and subtract.
84      */
signedAdd(SignedMutableBigInteger addend)85     void signedAdd(SignedMutableBigInteger addend) {
86         if (sign == addend.sign)
87             add(addend);
88         else
89             sign = sign * subtract(addend);
90 
91     }
92 
93    /**
94      * Signed addition built upon unsigned add and subtract.
95      */
signedAdd(MutableBigInteger addend)96     void signedAdd(MutableBigInteger addend) {
97         if (sign == 1)
98             add(addend);
99         else
100             sign = sign * subtract(addend);
101 
102     }
103 
104    /**
105      * Signed subtraction built upon unsigned add and subtract.
106      */
signedSubtract(SignedMutableBigInteger addend)107     void signedSubtract(SignedMutableBigInteger addend) {
108         if (sign == addend.sign)
109             sign = sign * subtract(addend);
110         else
111             add(addend);
112 
113     }
114 
115    /**
116      * Signed subtraction built upon unsigned add and subtract.
117      */
signedSubtract(MutableBigInteger addend)118     void signedSubtract(MutableBigInteger addend) {
119         if (sign == 1)
120             sign = sign * subtract(addend);
121         else
122             add(addend);
123         if (intLen == 0)
124              sign = 1;
125     }
126 
127     /**
128      * Print out the first intLen ints of this MutableBigInteger's value
129      * array starting at offset.
130      */
toString()131     public String toString() {
132         return this.toBigInteger(sign).toString();
133     }
134 
135 }
136