nim-codex/codex/indexingstrategy.nim

111 lines
2.8 KiB
Nim

import ./errors
import ./utils
import ./utils/asynciter
{.push raises: [].}
type
StrategyType* = enum
# Simplest approach:
# 0 => 0, 1, 2
# 1 => 3, 4, 5
# 2 => 6, 7, 8
LinearStrategy,
# Stepped indexing:
# 0 => 0, 3, 6
# 1 => 1, 4, 7
# 2 => 2, 5, 8
SteppedStrategy
# Representing a strategy for grouping indices (of blocks usually)
# Given an interation-count as input, will produce a seq of
# selected indices.
IndexingError* = object of CodexError
IndexingWrongIndexError* = object of IndexingError
IndexingWrongIterationsError* = object of IndexingError
IndexingStrategy* = object
strategyType*: StrategyType
firstIndex*: int # Lowest index that can be returned
lastIndex*: int # Highest index that can be returned
iterations*: int # getIndices(iteration) will run from 0 ..< iterations
step*: int
func checkIteration(self: IndexingStrategy, iteration: int): void {.raises: [IndexingError].} =
if iteration >= self.iterations:
raise newException(
IndexingError,
"Indexing iteration can't be greater than or equal to iterations.")
proc getIter(first, last, step: int): Iter[int] =
var
finish = false
cur = first
func get(): int =
result = cur
cur += step
if cur > last:
finish = true
func isFinished(): bool =
finish
Iter.new(get, isFinished)
func getLinearIndicies(
self: IndexingStrategy,
iteration: int): Iter[int] {.raises: [IndexingError].} =
self.checkIteration(iteration)
let
first = self.firstIndex + iteration * (self.step + 1)
last = min(first + self.step, self.lastIndex)
getIter(first, last, 1)
func getSteppedIndicies(
self: IndexingStrategy,
iteration: int): Iter[int] {.raises: [IndexingError].} =
self.checkIteration(iteration)
let
first = self.firstIndex + iteration
last = self.lastIndex
getIter(first, last, self.iterations)
func getIndicies*(
self: IndexingStrategy,
iteration: int): Iter[int] {.raises: [IndexingError].} =
case self.strategyType
of StrategyType.LinearStrategy:
self.getLinearIndicies(iteration)
of StrategyType.SteppedStrategy:
self.getSteppedIndicies(iteration)
func init*(
strategy: StrategyType,
firstIndex, lastIndex, iterations: int): IndexingStrategy {.raises: [IndexingError].} =
if firstIndex > lastIndex:
raise newException(
IndexingWrongIndexError,
"firstIndex (" & $firstIndex & ") can't be greater than lastIndex (" & $lastIndex & ")")
if iterations <= 0:
raise newException(
IndexingWrongIterationsError,
"iterations (" & $iterations & ") must be greater than zero.")
IndexingStrategy(
strategyType: strategy,
firstIndex: firstIndex,
lastIndex: lastIndex,
iterations: iterations,
step: divUp((lastIndex - firstIndex), iterations))