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<Chapter Label="Integers">
<Heading>Integers</Heading>

One of the most fundamental datatypes in every programming language is
the integer type.  &GAP; is no exception.
<P/>
&GAP; integers are entered as a sequence of decimal digits optionally
preceded by a <Q><C>+</C></Q> sign for positive integers or
a <Q><C>-</C></Q> sign for negative integers.
The size of integers in &GAP; is only limited by the amount of available
memory, so you can compute with integers having thousands of digits.
<P/>
<Example><![CDATA[
gap> -1234;
-1234
gap> 123456789012345678901234567890123456789012345678901234567890;
123456789012345678901234567890123456789012345678901234567890
]]></Example>

Note that in a few places, only certain small integer values can be used. A
<E>small integer</E> (also referred to as <E>immediate integer</E>) is an
integer <M>n</M> satisfying <C>INTOBJ_MIN</C> <M> \leq n \leq </M>
<C>INTOBJ_MAX</C>, where <C>INTOBJ_MIN</C> and <C>INTOBJ_MAX</C> equal either
<M>-2^{28}</M> and <M>2^{28}-1</M> (on 32-bit systems) or <M>-2^{60}</M> and
<M>2^{60}-1</M> (on 64-bit systems).
<Index>small integer</Index>
<Index>immediate integer</Index>
<Index>INTOBJ_MIN</Index>
<Index>INTOBJ_MAX</Index>
For example, the elements of a range are restricted to small integers
(see <Ref Sect="Ranges"/>).
<P/>

Many more functions that are mainly related to the prime residue group of
integers modulo an integer are described in chapter <Ref Chap="Number Theory"/>,
and functions dealing with combinatorics can be found
in chapter <Ref Chap="Combinatorics"/>.


<Section Label="sect:Integers: Global Variables">
<Heading>Integers: Global Variables</Heading>

<#Include Label="IntegersGlobalVars">
<#Include Label="IsIntegers">

</Section>


<Section Label="Elementary Operations for Integers">
<Heading>Elementary Operations for Integers</Heading>

<#Include Label="IsInt">
<#Include Label="IsPosInt">
<#Include Label="Int">
<#Include Label="IsEvenInt">
<#Include Label="IsOddInt">
<#Include Label="AbsInt">
<#Include Label="SignInt">
<#Include Label="LogInt">
<#Include Label="RootInt">
<#Include Label="SmallestRootInt">
<#Include Label="IsSquareInt">
<#Include Label="ListOfDigits">

<ManSection>
<Meth Name="Random" Arg='Integers' Label="for integers"/>

<Description>
<Ref Meth="Random" Label="for integers"/> for integers returns
pseudo random integers between <M>-10</M> and
<M>10</M> distributed according to a binomial distribution.
To generate uniformly distributed integers from a range,
use the construction <C>Random( [ <A>low</A> .. <A>high</A> ] )</C>
(see <Ref Oper="Random" Label="for lower and upper bound"/>).
</Description>
</ManSection>

</Section>


<Section Label="Quotients and Remainders">
<Heading>Quotients and Remainders</Heading>

<#Include Label="QuoInt">
<#Include Label="BestQuoInt">
<#Include Label="RemInt">
<#Include Label="GcdInt">
<#Include Label="Gcdex">
<#Include Label="LcmInt">
<#Include Label="CoefficientsQadic">
<#Include Label="CoefficientsMultiadic">
<#Include Label="ChineseRem">
<#Include Label="PowerModInt">

</Section>


<Section Label="Prime Integers and Factorization">
<Heading>Prime Integers and Factorization</Heading>

<#Include Label="Primes">
<#Include Label="IsPrimeInt">
<#Include Label="PrimalityProof">
<#Include Label="IsPrimePowerInt">
<#Include Label="NextPrimeInt">
<#Include Label="PrevPrimeInt">
<#Include Label="FactorsInt">
<#Include Label="PrimeDivisors">
<#Include Label="PartialFactorization">
<#Include Label="PrintFactorsInt">
<#Include Label="PrimePowersInt">
<#Include Label="DivisorsInt">

</Section>


<Section Label="Residue Class Rings">
<Heading>Residue Class Rings</Heading>

<Index Key="mod" Subkey="residue class rings"><K>mod</K></Index>
<Index Subkey="residue class rings">modulo</Index>
<Ref Func="ZmodnZ"/> returns a residue class ring of <Ref Var="Integers"/>
modulo an ideal.
These residue class rings are rings, thus all operations for rings
(see Chapter <Ref Chap="Rings"/>) apply.
See also Chapters <Ref Chap="Finite Fields"/> and
<Ref Chap="Number Theory"/>.

<ManSection>
<Oper Name="\mod" Arg="r/s, n" Label="for residue class rings"/>
<Description>
If <A>r</A>, <A>s</A> and <A>n</A> are integers, <C><A>r</A> / <A>s</A></C> as a  reduced  fraction  is
<C>p/q</C>, where <C>q</C> and <A>n</A> are coprime, then <C><A>r</A> / <A>s</A> mod <A>n</A></C>  is
defined to be the product of <C>p</C> and the inverse of <C>q</C> modulo  <A>n</A>. See
Section <Ref Sect="Arithmetic Operators"/> for more details and definitions.
<P/>
With the above definition, <C>4 / 6 mod 32</C> equals <C>2 / 3 mod 32</C> and hence
exists (and is equal to 22), despite the  fact  that  6  has  no  inverse
modulo 32.
</Description>
</ManSection>

<#Include Label="ZmodnZ">
<#Include Label="ZmodnZObj">
<#Include Label="IsZmodnZObj">

</Section>


<Section Label="Check Digits">
<Heading>Check Digits</Heading>

<#Include Label="CheckDigitISBN">
<#Include Label="CheckDigitTestFunction">

</Section>


<Section Label="Random Sources">
<Heading>Random Sources</Heading>

&GAP; provides <Ref Oper="Random" Label="for a list or collection"/> methods
for many collections of objects.
On a lower level these methods use <E>random sources</E> which provide
random integers and random choices from lists.
<P/>
See <Ref Filt="IsRandomSource"/> for the user interface for random sources,
and Section <Ref Subsect="Implementing new kinds of random sources"/>
for information about developing new kinds of random sources.

<#Include Label="IsRandomSource">
<#Include Label="Random">
<#Include Label="State">
<#Include Label="IsGlobalRandomSource">
<#Include Label="RandomSource">
<#Include Label="RandomSource_develop">

</Section>

<Section Label="Bitfields">
  <Heading>Bitfields</Heading>
Bitfields are a low-level feature intended to support efficient
subdivision of immediate integers into bitfields of various widths.
This is typically useful in implementing space-efficient and/or
cache-efficient data structures. This feature should be used with care
because (<E>inter alia</E>) it has different limitations on 32-bit and 64-bit
architectures.

<#Include Label="MakeBitfields">
<#Include Label="BuildBitfields">

</Section>

</Chapter>

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