1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
|
#
#
# 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 `queue`:idx:. The underlying implementation uses a ``seq``.
##
## None of the procs that get an individual value from the queue can be used
## on an empty queue.
## 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 queue 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 q = initQueue[int]() # initializes the object
## for i in 1 ..< a: q.add i # populates the queue
##
## if b < q.len: # checking before indexed access
## echo "The element at index position ", b, " is ", q[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 q.front == 1
## assert q.back == a
##
## while q.len > 0: # checking if the queue is empty
## echo q.pop()
##
## Note: For inter thread communication use
## a `Channel <channels.html>`_ instead.
import math
type
Queue*[T] = object ## A queue.
data: seq[T]
rd, wr, count, mask: int
{.deprecated: [TQueue: Queue].}
proc initQueue*[T](initialSize: int = 4): Queue[T] =
## Create a new queue.
## Optionally, the initial capacity can be reserved via `initialSize` as a
## performance optimization. The length of a newly created queue 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](q: Queue[T]): int {.inline.}=
## Return the number of elements of `q`.
result = q.count
template emptyCheck(q) =
# Bounds check for the regular queue access.
when compileOption("boundChecks"):
if unlikely(q.count < 1):
raise newException(IndexError, "Empty queue.")
template xBoundsCheck(q, i) =
# Bounds check for the array like accesses.
when compileOption("boundChecks"): # d:release should disable this.
if unlikely(i >= q.count): # x < q.low is taken care by the Natural parameter
raise newException(IndexError,
"Out of bounds: " & $i & " > " & $(q.count - 1))
proc front*[T](q: Queue[T]): T {.inline.}=
## Return the oldest element of `q`. Equivalent to `q.pop()` but does not
## remove it from the queue.
emptyCheck(q)
result = q.data[q.rd]
proc back*[T](q: Queue[T]): T {.inline.} =
## Return the newest element of `q` but does not remove it from the queue.
emptyCheck(q)
result = q.data[q.wr - 1 and q.mask]
proc `[]`*[T](q: Queue[T], i: Natural) : T {.inline.} =
## Access the i-th element of `q` by order of insertion.
## q[0] is the oldest (the next one q.pop() will extract),
## q[^1] is the newest (last one added to the queue).
xBoundsCheck(q, i)
return q.data[q.rd + i and q.mask]
proc `[]`*[T](q: var Queue[T], i: Natural): var T {.inline.} =
## Access the i-th element of `q` and returns a mutable
## reference to it.
xBoundsCheck(q, i)
return q.data[q.rd + i and q.mask]
proc `[]=`* [T] (q: var Queue[T], i: Natural, val : T) {.inline.} =
## Change the i-th element of `q`.
xBoundsCheck(q, i)
q.data[q.rd + i and q.mask] = val
iterator items*[T](q: Queue[T]): T =
## Yield every element of `q`.
var i = q.rd
for c in 0 ..< q.count:
yield q.data[i]
i = (i + 1) and q.mask
iterator mitems*[T](q: var Queue[T]): var T =
## Yield every element of `q`.
var i = q.rd
for c in 0 ..< q.count:
yield q.data[i]
i = (i + 1) and q.mask
iterator pairs*[T](q: Queue[T]): tuple[key: int, val: T] =
## Yield every (position, value) of `q`.
var i = q.rd
for c in 0 ..< q.count:
yield (c, q.data[i])
i = (i + 1) and q.mask
proc contains*[T](q: Queue[T], item: T): bool {.inline.} =
## Return true if `item` is in `q` or false if not found. Usually used
## via the ``in`` operator. It is the equivalent of ``q.find(item) >= 0``.
##
## .. code-block:: Nim
## if x in q:
## assert q.contains x
for e in q:
if e == item: return true
return false
proc add*[T](q: var Queue[T], item: T) =
## Add an `item` to the end of the queue `q`.
var cap = q.mask+1
if unlikely(q.count >= cap):
var n = newSeq[T](cap*2)
for i, x in q: # don't use copyMem because the GC and because it's slower.
shallowCopy(n[i], x)
shallowCopy(q.data, n)
q.mask = cap*2 - 1
q.wr = q.count
q.rd = 0
inc q.count
q.data[q.wr] = item
q.wr = (q.wr + 1) and q.mask
proc default[T](t: typedesc[T]): T {.inline.} = discard
proc pop*[T](q: var Queue[T]): T {.inline, discardable.} =
## Remove and returns the first (oldest) element of the queue `q`.
emptyCheck(q)
dec q.count
result = q.data[q.rd]
q.data[q.rd] = default(type(result))
q.rd = (q.rd + 1) and q.mask
proc enqueue*[T](q: var Queue[T], item: T) =
## Alias for the ``add`` operation.
q.add(item)
proc dequeue*[T](q: var Queue[T]): T =
## Alias for the ``pop`` operation.
q.pop()
proc `$`*[T](q: Queue[T]): string =
## Turn a queue into its string representation.
result = "["
for x in items(q): # Don't remove the items here for reasons that don't fit in this margin.
if result.len > 1: result.add(", ")
result.add($x)
result.add("]")
when isMainModule:
var q = initQueue[int](1)
q.add(123)
q.add(9)
q.enqueue(4)
var first = q.dequeue()
q.add(56)
q.add(6)
var second = q.pop()
q.add(789)
assert first == 123
assert second == 9
assert($q == "[4, 56, 6, 789]")
assert q[0] == q.front and q.front == 4
assert q[^1] == q.back and q.back == 789
q[0] = 42
q[^1] = 7
assert 6 in q and 789 notin q
assert q.find(6) >= 0
assert q.find(789) < 0
for i in -2 .. 10:
if i in q:
assert q.contains(i) and q.find(i) >= 0
else:
assert(not q.contains(i) and q.find(i) < 0)
when compileOption("boundChecks"):
try:
echo q[99]
assert false
except IndexError:
discard
try:
assert q.len == 4
for i in 0 ..< 5: q.pop()
assert false
except IndexError:
discard
# grabs some types of resize error.
q = initQueue[int]()
for i in 1 .. 4: q.add i
q.pop()
q.pop()
for i in 5 .. 8: q.add i
assert $q == "[3, 4, 5, 6, 7, 8]"
# Similar to proc from the documentation example
proc foo(a, b: Positive) = # assume random positive values for `a` and `b`.
var q = initQueue[int]()
assert q.len == 0
for i in 1 .. a: q.add i
if b < q.len: # checking before indexed access.
assert q[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 q.front == 1
assert q.back == a
while q.len > 0: # checking if the queue is empty
assert q.pop() > 0
#foo(0,0)
foo(8,5)
foo(10,9)
foo(1,1)
foo(2,1)
foo(1,5)
foo(3,2)
|