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# Source file src/math/big/doc.go

## Documentation: math/big

```     1  // Copyright 2009 The Go Authors. All rights reserved.
2  // Use of this source code is governed by a BSD-style
4
5  /*
6  Package big implements arbitrary-precision arithmetic (big numbers).
7  The following numeric types are supported:
8
9  	Int    signed integers
10  	Rat    rational numbers
11  	Float  floating-point numbers
12
13  The zero value for an Int, Rat, or Float correspond to 0. Thus, new
14  values can be declared in the usual ways and denote 0 without further
15  initialization:
16
17  	var x Int        // &x is an *Int of value 0
18  	var r = &Rat{}   // r is a *Rat of value 0
19  	y := new(Float)  // y is a *Float of value 0
20
21  Alternatively, new values can be allocated and initialized with factory
22  functions of the form:
23
24  	func NewT(v V) *T
25
26  For instance, NewInt(x) returns an *Int set to the value of the int64
27  argument x, NewRat(a, b) returns a *Rat set to the fraction a/b where
28  a and b are int64 values, and NewFloat(f) returns a *Float initialized
29  to the float64 argument f. More flexibility is provided with explicit
30  setters, for instance:
31
32  	var z1 Int
33  	z1.SetUint64(123)                 // z1 := 123
34  	z2 := new(Rat).SetFloat64(1.25)   // z2 := 5/4
35  	z3 := new(Float).SetInt(z1)       // z3 := 123.0
36
37  Setters, numeric operations and predicates are represented as methods of
38  the form:
39
40  	func (z *T) SetV(v V) *T          // z = v
41  	func (z *T) Unary(x *T) *T        // z = unary x
42  	func (z *T) Binary(x, y *T) *T    // z = x binary y
43  	func (x *T) Pred() P              // p = pred(x)
44
45  with T one of Int, Rat, or Float. For unary and binary operations, the
46  result is the receiver (usually named z in that case; see below); if it
47  is one of the operands x or y it may be safely overwritten (and its memory
48  reused).
49
50  Arithmetic expressions are typically written as a sequence of individual
51  method calls, with each call corresponding to an operation. The receiver
52  denotes the result and the method arguments are the operation's operands.
53  For instance, given three *Int values a, b and c, the invocation
54
56
57  computes the sum a + b and stores the result in c, overwriting whatever
58  value was held in c before. Unless specified otherwise, operations permit
59  aliasing of parameters, so it is perfectly ok to write
60
62
63  to accumulate values x in a sum.
64
65  (By always passing in a result value via the receiver, memory use can be
66  much better controlled. Instead of having to allocate new memory for each
67  result, an operation can reuse the space allocated for the result value,
68  and overwrite that value with the new result in the process.)
69
70  Notational convention: Incoming method parameters (including the receiver)
71  are named consistently in the API to clarify their use. Incoming operands
72  are usually named x, y, a, b, and so on, but never z. A parameter specifying
73  the result is named z (typically the receiver).
74
75  For instance, the arguments for (*Int).Add are named x and y, and because
76  the receiver specifies the result destination, it is called z:
77
78  	func (z *Int) Add(x, y *Int) *Int
79
80  Methods of this form typically return the incoming receiver as well, to
81  enable simple call chaining.
82
83  Methods which don't require a result value to be passed in (for instance,
84  Int.Sign), simply return the result. In this case, the receiver is typically
85  the first operand, named x:
86
87  	func (x *Int) Sign() int
88
89  Various methods support conversions between strings and corresponding
90  numeric values, and vice versa: *Int, *Rat, and *Float values implement
91  the Stringer interface for a (default) string representation of the value,
92  but also provide SetString methods to initialize a value from a string in
93  a variety of supported formats (see the respective SetString documentation).
94
95  Finally, *Int, *Rat, and *Float satisfy the fmt package's Scanner interface
96  for scanning and (except for *Rat) the Formatter interface for formatted
97  printing.
98  */
99  package big
100
```

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