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ENH add an introsort implementation #7

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ENH add an introsort implementation #7

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59 changes: 56 additions & 3 deletions src/SortingAlgorithms.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -8,15 +8,17 @@ import
Base.Collections.heapify!,
Base.Collections.percolate_down!

export HeapSort, TimSort, RadixSort
export HeapSort, IntroSort, RadixSort, TimSort

immutable HeapSortAlg <: Algorithm end
immutable TimSortAlg <: Algorithm end
immutable IntroSortAlg <: Algorithm end
immutable RadixSortAlg <: Algorithm end
immutable TimSortAlg <: Algorithm end

const HeapSort = HeapSortAlg()
const TimSort = TimSortAlg()
const IntroSort = IntroSortAlg()
const RadixSort = RadixSortAlg()
const TimSort = TimSortAlg()


## Heap sort
Expand Down Expand Up @@ -560,4 +562,55 @@ function sort!(v::AbstractVector, lo::Int, hi::Int, ::TimSortAlg, o::Ordering)
return v
end


## Intro sort

function sort!(v::AbstractVector, lo::Int, hi::Int, a::IntroSortAlg, o::Ordering)
N = length(v)
if N > 1
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this guard should rather be on hi - lo > 1 (which can cause an exception due to log2(...) == -Inf).

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Hmmm, I wonder what this comment meant...

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It's referring to the line below, and I think that's right. Care to submit a pull request?

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So this line should just be hi-li > 1, will see if that works and push an update commit here.

Any thoughts on optimizations for index_of_median_of_three ?

introsort_loop!(v, lo, hi, 2 * ifloor(log2(hi - lo + 1)), o)
sort!(v, lo, hi, InsertionSort, o)
end
v
end

function introsort_loop!(v::AbstractVector, lo::Int, hi::Int, depth_limit::Int, o::Ordering)
while hi - lo > depth_limit
if depth_limit == 0
sort!(v, lo, hi, HeapSort, o)
return v
end
depth_limit -= 1
p = partition!(v, lo, hi, index_of_median_of_three(v, lo, hi, o), o)
introsort_loop!(v, p, hi, depth_limit, o)
hi = p
end
v
end

function partition!(v::AbstractVector, lo::Int, hi::Int, p::Int, o::Ordering)
val = v[p]
v[p], v[hi] = v[hi], v[p]
j = lo
for i in lo:hi
if lt(o, v[i], val)
v[i], v[j] = v[j], v[i]
j += 1
end
end
v[j], v[hi] = v[hi], v[j]
return j
end

function index_of_median_of_three(v, lo, hi, o)
middle = lo + div(hi - lo, 2)
if lt(o, v[lo], v[middle])
return lt(o, v[middle], v[hi]) ? middle : hi
elseif lt(o, v[hi], v[middle])
return middle
else
return lt(o, v[lo], v[hi]) ? lo : hi
end
end

end # module
4 changes: 2 additions & 2 deletions test/runtests.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@ using SortingAlgorithms

a = rand(1:10000, 1000)

for alg in {TimSort, HeapSort, RadixSort}
for alg in {HeapSort, IntroSort, RadixSort, TimSort}
b = sort(a, alg=alg)
@test issorted(b)
ix = sortperm(a, alg=alg)
Expand Down Expand Up @@ -83,7 +83,7 @@ for n in [0:10, 100, 101, 1000, 1001]
end

# unstable algorithms
for alg in [HeapSort]
for alg in [HeapSort, IntroSort]
p = sortperm(v, alg=alg, order=ord)
@test isperm(p)
@test v[p] == si
Expand Down