1 // Copyright 2009 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
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 55 c.Add(a, b)
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 61 sum.Add(sum, x)
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 [fmt.Scanner] for scanning
96 and (except for *[Rat]) the Formatter interface for formatted printing.
97 */
98 package big
99