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Faster radix sort #48459

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745ec38
Faster radix sort
LSchwerdt Jan 30, 2023
62d234b
Remove superfluous white space
LSchwerdt Jan 30, 2023
cb97f9f
Use Cartesian.@nexprs instead of custom macro
LSchwerdt Jan 30, 2023
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26 changes: 23 additions & 3 deletions base/sort.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -1112,6 +1112,13 @@ function radix_sort!(v::AbstractVector{U}, lo::Integer, hi::Integer, bits::Unsig
shift < bits || return true
end
end

macro repeat4x(a)
quote
$a; $a; $a; $a
end |> esc
end

function radix_sort_pass!(t, lo, hi, offset, counts, v, shift, chunk_size)
mask = UInt(1) << chunk_size - 1 # mask is defined in pass so that the compiler
@inbounds begin # ↳ knows it's shape
Expand All @@ -1130,14 +1137,27 @@ function radix_sort_pass!(t, lo, hi, offset, counts, v, shift, chunk_size)
# belongs, not the number of elements in each bucket. We will put the first element
# of bucket 0x00 in t[counts[1]], the next element of bucket 0x00 in t[counts[1]+1],
# and the last element of bucket 0x00 in t[counts[2]-1].

for k in lo:hi

#loop unrolled 4x
k = lo
while k <= hi - 4
@repeat4x begin
x = v[k] # lookup the element
i = (x >> shift)&mask + 1 # compute its bucket's index for this pass
j = counts[i] # lookup the target index
t[j + offset] = x # put the element where it belongs
counts[i] = j + 1 # increment the target index for the next
k += 1 # ↳ element in this bucket
end
end
while k <= hi
x = v[k] # lookup the element
i = (x >> shift)&mask + 1 # compute its bucket's index for this pass
j = counts[i] # lookup the target index
t[j + offset] = x # put the element where it belongs
counts[i] = j + 1 # increment the target index for the next
end # ↳ element in this bucket
k += 1 # ↳ element in this bucket
end
end
end
function radix_chunk_size_heuristic(lo::Integer, hi::Integer, bits::Unsigned)
Expand Down