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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
     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 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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