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#
#
# Nim's Runtime Library
# (c) Copyright 2012 Andreas Rumpf
#
# See the file "copying.txt", included in this
# distribution, for details about the copyright.
#
## Implementation of a `deque`:idx: (double-ended queue).
## The underlying implementation uses a ``seq``.
##
## None of the procs that get an individual value from the deque can be used
## on an empty deque.
## If compiled with `boundChecks` option, those procs will raise an `IndexError`
## on such access. This should not be relied upon, as `-d:release` will
## disable those checks and may return garbage or crash the program.
##
## As such, a check to see if the deque is empty is needed before any
## access, unless your program logic guarantees it indirectly.
##
## .. code-block:: Nim
## proc foo(a, b: Positive) = # assume random positive values for `a` and `b`
## var deq = initDeque[int]() # initializes the object
## for i in 1 ..< a: deq.addLast i # populates the deque
##
## if b < deq.len: # checking before indexed access
## echo "The element at index position ", b, " is ", deq[b]
##
## # The following two lines don't need any checking on access due to the
## # logic of the program, but that would not be the case if `a` could be 0.
## assert deq.peekFirst == 1
## assert deq.peekLast == a
##
## while deq.len > 0: # checking if the deque is empty
## echo deq.removeLast()
##
## Note: For inter thread communication use
## a `Channel <channels.html>`_ instead.
import math
type
Deque*[T] = object
## A double-ended queue backed with a ringed seq buffer.
data: seq[T]
head, tail, count, mask: int
proc initDeque*[T](initialSize: int = 4): Deque[T] =
## Create a new deque.
## Optionally, the initial capacity can be reserved via `initialSize` as a
## performance optimization. The length of a newly created deque will still
## be 0.
##
## `initialSize` needs to be a power of two. If you need to accept runtime
## values for this you could use the ``nextPowerOfTwo`` proc from the
## `math <math.html>`_ module.
assert isPowerOfTwo(initialSize)
result.mask = initialSize-1
newSeq(result.data, initialSize)
proc len*[T](deq: Deque[T]): int {.inline.} =
## Return the number of elements of `deq`.
result = deq.count
template emptyCheck(deq) =
# Bounds check for the regular deque access.
when compileOption("boundChecks"):
if unlikely(deq.count < 1):
raise newException(IndexError, "Empty deque.")
template xBoundsCheck(deq, i) =
# Bounds check for the array like accesses.
when compileOption("boundChecks"): # d:release should disable this.
if unlikely(i >= deq.count): # x < deq.low is taken care by the Natural parameter
raise newException(IndexError,
"Out of bounds: " & $i & " > " & $(deq.count - 1))
proc `[]`*[T](deq: Deque[T], i: Natural) : T {.inline.} =
## Access the i-th element of `deq` by order from first to last.
## deq[0] is the first, deq[^1] is the last.
xBoundsCheck(deq, i)
return deq.data[(deq.first + i) and deq.mask]
proc `[]`*[T](deq: var Deque[T], i: Natural): var T {.inline.} =
## Access the i-th element of `deq` and returns a mutable
## reference to it.
xBoundsCheck(deq, i)
return deq.data[(deq.head + i) and deq.mask]
proc `[]=`* [T] (deq: var Deque[T], i: Natural, val : T) {.inline.} =
## Change the i-th element of `deq`.
xBoundsCheck(deq, i)
deq.data[(deq.head + i) and deq.mask] = val
iterator items*[T](deq: Deque[T]): T =
## Yield every element of `deq`.
var i = deq.head
for c in 0 ..< deq.count:
yield deq.data[i]
i = (i + 1) and deq.mask
iterator mitems*[T](deq: var Deque[T]): var T =
## Yield every element of `deq`.
var i = deq.head
for c in 0 ..< deq.count:
yield deq.data[i]
i = (i + 1) and deq.mask
iterator pairs*[T](deq: Deque[T]): tuple[key: int, val: T] =
## Yield every (position, value) of `deq`.
var i = deq.head
for c in 0 ..< deq.count:
yield (c, deq.data[i])
i = (i + 1) and deq.mask
proc contains*[T](deq: Deque[T], item: T): bool {.inline.} =
## Return true if `item` is in `deq` or false if not found. Usually used
## via the ``in`` operator. It is the equivalent of ``deq.find(item) >= 0``.
##
## .. code-block:: Nim
## if x in q:
## assert q.contains x
for e in deq:
if e == item: return true
return false
proc expandIfNeeded[T](deq: var Deque[T]) =
var cap = deq.mask + 1
if unlikely(deq.count >= cap):
var n = newSeq[T](cap * 2)
for i, x in deq: # don't use copyMem because the GC and because it's slower.
shallowCopy(n[i], x)
shallowCopy(deq.data, n)
deq.mask = cap * 2 - 1
deq.tail = deq.count
deq.head = 0
proc addFirst*[T](deq: var Deque[T], item: T) =
## Add an `item` to the beginning of the `deq`.
expandIfNeeded(deq)
inc deq.count
deq.head = (deq.head - 1) and deq.mask
deq.data[deq.head] = item
proc addLast*[T](deq: var Deque[T], item: T) =
## Add an `item` to the end of the `deq`.
expandIfNeeded(deq)
inc deq.count
deq.data[deq.tail] = item
deq.tail = (deq.tail + 1) and deq.mask
proc peekFirst*[T](deq: Deque[T]): T {.inline.}=
## Returns the first element of `deq`, but does not remove it from the deque.
emptyCheck(deq)
result = deq.data[deq.head]
proc peekLast*[T](deq: Deque[T]): T {.inline.} =
## Returns the last element of `deq`, but does not remove it from the deque.
emptyCheck(deq)
result = deq.data[(deq.tail - 1) and deq.mask]
proc default[T](t: typedesc[T]): T {.inline.} = discard
proc popFirst*[T](deq: var Deque[T]): T {.inline, discardable.} =
## Remove and returns the first element of the `deq`.
emptyCheck(deq)
dec deq.count
result = deq.data[deq.head]
deq.data[deq.head] = default(type(result))
deq.head = (deq.head + 1) and deq.mask
proc popLast*[T](deq: var Deque[T]): T {.inline, discardable.} =
## Remove and returns the last element of the `deq`.
emptyCheck(deq)
dec deq.count
deq.tail = (deq.tail - 1) and deq.mask
result = deq.data[deq.tail]
deq.data[deq.tail] = default(type(result))
proc `$`*[T](deq: Deque[T]): string =
## Turn a deque into its string representation.
result = "["
for x in deq:
if result.len > 1: result.add(", ")
result.add($x)
result.add("]")
when isMainModule:
var deq = initDeque[int](1)
deq.addLast(4)
deq.addFirst(9)
deq.addFirst(123)
var first = deq.popFirst()
deq.addLast(56)
assert(deq.peekLast() == 56)
deq.addLast(6)
assert(deq.peekLast() == 6)
var second = deq.popFirst()
deq.addLast(789)
assert(deq.peekLast() == 789)
assert first == 123
assert second == 9
assert($deq == "[4, 56, 6, 789]")
assert deq[0] == deq.peekFirst and deq.peekFirst == 4
assert deq[^1] == deq.peekLast and deq.peekLast == 789
deq[0] = 42
deq[^1] = 7
assert 6 in deq and 789 notin deq
assert deq.find(6) >= 0
assert deq.find(789) < 0
for i in -2 .. 10:
if i in deq:
assert deq.contains(i) and deq.find(i) >= 0
else:
assert(not deq.contains(i) and deq.find(i) < 0)
when compileOption("boundChecks"):
try:
echo deq[99]
assert false
except IndexError:
discard
try:
assert deq.len == 4
for i in 0 ..< 5: deq.popFirst()
assert false
except IndexError:
discard
# grabs some types of resize error.
deq = initDeque[int]()
for i in 1 .. 4: deq.addLast i
deq.popFirst()
deq.popLast()
for i in 5 .. 8: deq.addFirst i
assert $deq == "[8, 7, 6, 5, 2, 3]"
# Similar to proc from the documentation example
proc foo(a, b: Positive) = # assume random positive values for `a` and `b`.
var deq = initDeque[int]()
assert deq.len == 0
for i in 1 .. a: deq.addLast i
if b < deq.len: # checking before indexed access.
assert deq[b] == b + 1
# The following two lines don't need any checking on access due to the logic
# of the program, but that would not be the case if `a` could be 0.
assert deq.peekFirst == 1
assert deq.peekLast == a
while deq.len > 0: # checking if the deque is empty
assert deq.popFirst() > 0
#foo(0,0)
foo(8,5)
foo(10,9)
foo(1,1)
foo(2,1)
foo(1,5)
foo(3,2)
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