Programming Ruby

The Pragmatic Programmer's Guide

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class Bignum
Parent: Integer
Version: 1.6


Arithmetic operations Bit operations <=> [ ] size to_f to_i to_s

Bignum objects hold integers outside the range of Fixnum. Bignum objects are created automatically when integer calculations would otherwise overflow a Fixnum. When a calculation involving Bignum objects returns a result that will fit in a Fixnum, the result is automatically converted.

For the purposes of the bitwise operations and [], a Bignum is treated as if it were an infinite-length bitstring with 2's complement representation.

While Fixnum values are immediate, Bignum objects are not---assignment and parameter passing work with references to objects, not the objects themselves.

instance methods
Arithmetic operations

Performs various arithmetic operations on big.

big + aNumeric Addition
big -- aNumeric Subtraction
big * aNumeric Multiplication
big / aNumeric Division
big % aNumeric Modulo
big ** aNumeric Exponentiation

Bit operations

Performs various operations on the binary representations of the Bignum

~ big Invert bits
big | aNumeric Bitwise OR
big & aNumeric Bitwise AND
big ^ aNumeric Bitwise EXCLUSIVE OR
big << aNumeric Left-shift aNumeric bits
big >> aNumeric Right-shift aNumeric bits (with sign extension)

<=> big <=> aNumeric -> -1, 0, +1

Comparison---Returns -1, 0, or +1 depending on whether big is less than, equal to, or greater than aNumeric. This is the basis for the tests in Comparable.

[ ] big[ n ] -> 0, 1

Bit Reference---Returns the nth bit in the (assumed) binary representation of big, where big[0] is the least significant bit.

a = 9**15
50.downto(0) do |n|
  print a[n]

size big.size -> anInteger

Returns the number of bytes in the machine representation of big.

(256**10 - 1).size 12
(256**20 - 1).size 20
(256**40 - 1).size 40

to_f big.to_f -> aFloat

Converts big to a Float. If big doesn't fit in a Float, the result is infinity.

to_i big.to_i -> big

Returns big.

to_s big.to_s -> aString

Returns a string containing the decimal representation of big.

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Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
Copyright © 2001 by Addison Wesley Longman, Inc. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at

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