"

 COPYRIGHT (c) 1989 by Claus Gittinger

              All Rights Reserved

 This software is furnished under a license and may be used

 only in accordance with the terms of that license and with the

 inclusion of the above copyright notice.   This software may not

 be provided or otherwise made available to, or used by, any

 other person.  No title to or ownership of the software is

 hereby transferred.

"

"{ Package: 'stx:libbasic' }"

"{ NameSpace: Smalltalk }"

ReadOnlySequenceableCollection subclass:#Interval

	instanceVariableNames:'start stop step'

	classVariableNames:''

	poolDictionaries:''

	category:'Collections-Sequenceable'

!

!Interval class methodsFor:'documentation'!

copyright

"

 COPYRIGHT (c) 1989 by Claus Gittinger

              All Rights Reserved

 This software is furnished under a license and may be used

 only in accordance with the terms of that license and with the

 inclusion of the above copyright notice.   This software may not

 be provided or otherwise made available to, or used by, any

 other person.  No title to or ownership of the software is

 hereby transferred.

"

!

documentation

"

    Intervals represent a collection (or range) of numeric values specified by

    a startValue, an endValue and a step. 

    The interesting thing is that the elements are computed, not stored.

    However, protocol-wise, intervals behave like any other (read-only) sequenceable collection.

    For example, the interval (1 to:5) containes the elements (1 2 3 4 5) and

    (1 to:6 by:2) contains (1 3 5).

    The step may be negative, to count backward:

    (5 to:1 by:-1) contains (5 4 3 2 1), and (6 to:1 by:-2) contains (6 4 2).

    examples:

        (1 to:10) do:[:i | Transcript showCR:i]

      notice, that this is semantically equivalent to:

        1 to:10 do:[:i | Transcript showCR:i]

      however, the second is preferred, since loops using to:do: are

      much faster and do not create temporary garbage objects. 

      Therefore, Intervals are generally NOT used for this kind of loops.

        (1 to:10) asArray  

        (1 to:10 by:2) asOrderedCollection  

    [author:]

        Claus Gittinger

"

! !

!Interval class methodsFor:'instance creation'!

from:start to:stop

    "return a new interval with elements from start to stop by 1"

    ^ self new setFrom:start to:stop by:1

!

from:start to:stop by:step

    "return a new interval with elements from start to stop by step"

    ^ self new setFrom:start to:stop by:step

! !

!Interval class methodsFor:'converting'!

decodeFromLiteralArray:anArray

    "create & return a new instance from information encoded in anArray.

     Re-redefined, since the implementation in SequencableCollection creates instances with an initial

     size, which is not allowed for intervals."

    ^ self new fromLiteralArrayEncoding:anArray.

! !

!Interval methodsFor:'accessing'!

at:index

    "return (i.e. compute) the index'th element"

    (index between:1 and:self size) ifTrue:[

        ^ start + (step * (index - 1))

    ].

    ^ self subscriptBoundsError:index

!

first

    "return the first element of the collection"

    (((step < 0) and:[start < stop])

    or:[(step > 0) and:[stop < start]]) ifTrue:[

        ^ self emptyCollectionError

    ].

    ^ start

!

increment 

    "alias for #step; for ST-80 compatibility"

    ^ step

!

last

    "return the last element of the collection"

    (((step < 0) and:[start < stop])

    or:[(step > 0) and:[stop < start]]) ifTrue:[

        ^ self emptyCollectionError

    ].

    ^ stop

!

start

    "return the first number of the range"

    ^ start

!

start:aNumber

    "set the first number of the range"

    start := aNumber

!

step

    "return the step increment of the range.

     OBSOLETE: 

        Please use #increment for ST-80 compatibility."

    ^ step

!

step:aNumber

    "set the step increment of the range"

    step := aNumber

!

stop

    "return the end number of the range"

    ^ stop

!

stop:aNumber

    "set the end number of the range"

    stop := aNumber

! !

!Interval methodsFor:'bulk operations'!

sum

    "sum up all elements."

    "/              n*(n+1)

    "/ sum(1..n) is -------

    "/                 2

    start < stop ifTrue:[

        step == 1 ifTrue:[

            start == 1 ifTrue:[

                ^ (stop * (stop + 1) / 2)

            ].

            ^ (stop * (stop + 1) / 2) - ((start-1) * (start ) / 2)

        ]

    ].

    "/ could add more optimizations here, but who needs them?

    ^ super sum

    "

     (1 to:10) sum         

     (1 to:10) asArray sum 

     (2 to:10) sum           

     (2 to:10) asArray sum   

     (5 to:10) sum    

     (5 to:10) asArray sum     

    "

! !

!Interval methodsFor:'comparing'!

= anInterval

    anInterval class == self class ifTrue:[

        ^ start = anInterval start

        and:[ stop = anInterval stop

        and:[ step = anInterval step]]

    ].

    ^ super = anInterval

!

hash

    ^ super hash "/ do not redefine: must generate same hash as SeqColl.

! !

!Interval methodsFor:'converting'!

asInterval

    ^ self.

!

fromLiteralArrayEncoding:encoding

    "read my values from an encoding.

     The encoding is supposed to be either of the form: 

        (#Interval start stop step)

     This is the reverse operation to #literalArrayEncoding."

    start := (encoding at:2).

    stop := (encoding at:3). 

    (encoding size > 3) ifTrue:[ 

        step := (encoding at:4).

    ] ifFalse:[

        step := 1.

    ]

    "

     Interval new fromLiteralArrayEncoding:((1 to:10) literalArrayEncoding)  

     Interval new fromLiteralArrayEncoding:((1 to:10 by:2) literalArrayEncoding) 

     Interval decodeFromLiteralArray:((1 to:10 by:2) literalArrayEncoding) 

    "

!

literalArrayEncoding

    "encode myself as an array literal, from which a copy of the receiver

     can be reconstructed with #decodeAsLiteralArray."

    ^ Array

        with:self class name

        with:start

        with:stop

        with:step

    "

     (1 to:10) literalArrayEncoding      

     (1 to:10 by:2) literalArrayEncoding

    "

! !

!Interval methodsFor:'converting-reindexed'!

from:startIndex

    "return a new collection representing the receiver's elements starting at startIndex."

    step == 1 ifTrue:[

        ^ start+startIndex-1 to:stop

    ].

    "could be more intelligent here"

    ^ super from:startIndex

    "

     (1 to:100) from:2  

     (1 to:20 by:2) from:2           

     (1 to:20 by:2) asArray from:2    

     ((1 to:20 by:2) from:2) asArray   

    "

!

to:endIndex

    "return a new collection representing the receiver's elements upTo and including endIndex."

    ^ start to:(endIndex min:stop) by:step

    "

     (1 to:100) to:50    

     (1 to:100 by:2) to:50    

    "

! !

!Interval methodsFor:'enumerating'!

collect:aBlock

    "evaluate the argument, aBlock for every element in the collection

     and return a collection of the results.

     Redefined since the inherited method (SeqColl) accesses the receiver via at:, 

     which is slow for intervals"

    |elementValue mySize newCollection|

    elementValue := start.

    newCollection := self species newWithSize:(mySize := self size).

    1 to: mySize do:[:i |

        newCollection at:i put:(aBlock value:elementValue).

        elementValue := elementValue + step.

    ].

    ^ newCollection    

    "

     (1 to:20 by:2) collect:[:i | i*i]              

    "

    "Modified: / 04-05-2012 / 13:03:56 / cg"

!

do:aBlock

    "evaluate the argument, aBlock for every element in the receiver-interval. 

     Redefined since SeqColl accesses the receiver with at:, which is slow for intervals."

    |aValue iter|

    aValue := start.

    aValue isInteger ifTrue:[

        step < 0 ifTrue:[

            [stop <= aValue] whileTrue:[

                aBlock value:aValue.

                aValue := aValue + step

            ]

        ] ifFalse:[

            [stop >= aValue] whileTrue:[

                aBlock value:aValue.

                aValue := aValue + step

            ]

        ]

    ] ifFalse:[

        "/ the code below avoids rounding errors

        "/ to accumulate if floats are enumerated.

        iter := 1.

        step < 0 ifTrue:[

            [stop <= aValue] whileTrue:[

                aBlock value:aValue.

                aValue := start + (iter * step).

                iter := iter + 1.

            ]

        ] ifFalse:[

            [stop >= aValue] whileTrue:[

                aBlock value:aValue.

                aValue := start + (iter * step).

                iter := iter + 1.

            ]

        ]

    ]

    "

     1e7 to:1e7+1 by:0.25 do:[:v | Transcript showCR:v]

     1.0 to:2.0 by:0.25 do:[:v | Transcript showCR:v]

     2.0 to:1.0 by:-0.25 do:[:v | Transcript showCR:v]

     $a to:$z do:[:v | Transcript showCR:v]

    "

    "Modified: / 22-10-2008 / 12:47:30 / cg"

!

reverseDo:aBlock

    "evaluate the argument, aBlock for every element in the receiver-interval in

     reverse order. 

     Redefined since SeqColl accesses the receiver with at:, which is slow for intervals."

    ^ self reversed do:aBlock

    "

     (1 to:10) do:[:el | Transcript showCR:el ].

     (1 to:10) reverseDo:[:el | Transcript showCR:el ].

    "

    "Modified: / 22-10-2008 / 12:49:28 / cg"

!

select:aBlock

    "evaluate the argument, aBlock for every element in the collection

     and return a collection of all elements for which the block return true. 

     Redefined since SeqColl accesses the receiver with at:, which is slow for intervals."

    |newColl|

    newColl := self species new:(self size).

    self do:[:each |

        (aBlock value:each) ifTrue:[newColl add:each]

    ].

    ^ newColl

    "

     (1 to:20) select:[:i | i even]

    "

    "Modified: / 22-10-2008 / 12:47:41 / cg"

! !

!Interval methodsFor:'printing & storing'!

displayOn:aGCOrStream

    "/ what a kludge - Dolphin and Squeak mean: printOn: a stream;

    "/ ST/X (and some old ST80's) mean: draw-yourself on a GC.

    (aGCOrStream isStream) ifTrue:[

        self printOn:aGCOrStream.

        ^ self.

    ].

    ^ super displayOn:aGCOrStream

    "

     (1 to:10) 

     (1 to:10 by:2) 

    "

!

printOn:aStream

    "append a printed representation to aStream"

    start printOn:aStream.

    aStream nextPutAll:' to:'.

    stop printOn:aStream.

    step ~= 1 ifTrue:[

        aStream nextPutAll:' by:'.

        step printOn:aStream.

    ].

    "

     (1 to:10) printOn:Transcript

     (1 to:10 by:2) printOn:Transcript

     (1 to:10) printString

    "

!

storeOn:aStream

    "store a representation which can reconstruct the receiver to aStream"

    aStream nextPut:$(.

    self printOn:aStream.

    aStream nextPut:$).

    "

     (1 to:10) storeOn:Transcript

     (1 to:10 by:2) storeOn:Transcript

    "

! !

!Interval methodsFor:'private'!

setFrom:startInteger to:stopInteger by:stepInteger

    "set start, stop and step components"

    start := startInteger.

    stop := stopInteger.

    step := stepInteger

!

species

    "return the type of collection to be returned by collect, select etc."

    ^ OrderedCollection

! !

!Interval methodsFor:'queries'!

max

    "return the maximum value in the receiver collection,

     redefined, since this can be easily computed.

     Raises an error, if the receiver is empty."

    step == 1 ifTrue:[stop >= start ifTrue:[^ stop]].

    step < 0 ifTrue:[stop <= start ifTrue:[^ start]].

    ^ super max

    "

     (0 to:15) max           

     (0 to:15 by:2) max      

     (0 to:15 by:8) max      

     (15 to:0) max           -> error

     (15 to:0 by:4) max      -> error      

     (-1 to:-15 by:-1) max    

     (-1 to:-15 by:-4) max    

     (-1 to:15 by:-1) max    -> error  

    "