batteries/stable_sort.lua

155 lines
4.1 KiB
Lua

--[[
stable sorting routines
]]
--this is based on MIT licensed code from Dirk Laurie and Steve Fisher
--license as follows:
--[[
Copyright © 2013 Dirk Laurie and Steve Fisher.
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the "Software"),
to deal in the Software without restriction, including without limitation
the rights to use, copy, modify, merge, publish, distribute, sublicense,
and/or sell copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
]]
-- (modifications by Max Cahill 2018, 2020)
local sort_core = {}
--tunable size for insertion sort "bottom out"
sort_core.max_chunk_size = 32
--insertion sort on a section of array
function sort_core._insertion_sort_impl(array, first, last, less)
for i = first + 1, last do
local k = first
local v = array[i]
for j = i, first + 1, -1 do
if less(v, array[j - 1]) then
array[j] = array[j - 1]
else
k = j
break
end
end
array[k] = v
end
end
--merge sorted adjacent sections of array
function sort_core._merge(array, workspace, low, middle, high, less)
local i, j, k
i = 1
-- copy first half of array to auxiliary array
for j = low, middle do
workspace[i] = array[j]
i = i + 1
end
-- sieve through
i = 1
j = middle + 1
k = low
while true do
if (k >= j) or (j > high) then
break
end
if less(array[j], workspace[i]) then
array[k] = array[j]
j = j + 1
else
array[k] = workspace[i]
i = i + 1
end
k = k + 1
end
-- copy back any remaining elements of first half
for k = k, j - 1 do
array[k] = workspace[i]
i = i + 1
end
end
--implementation for the merge sort
function sort_core._merge_sort_impl(array, workspace, low, high, less)
if high - low <= sort_core.max_chunk_size then
sort_core._insertion_sort_impl(array, low, high, less)
else
local middle = math.floor((low + high) / 2)
sort_core._merge_sort_impl(array, workspace, low, middle, less)
sort_core._merge_sort_impl(array, workspace, middle + 1, high, less)
sort_core._merge(array, workspace, low, middle, high, less)
end
end
--default comparison; hoisted for clarity
local function default_less(a, b)
return a < b
end
--inline common setup stuff
function sort_core._sort_setup(array, less)
--default less
less = less or default_less
--
local n = #array
--trivial cases; empty or 1 element
local trivial = (n <= 1)
if not trivial then
--check less
if less(array[1], array[1]) then
error("invalid order function for sorting; less(v, v) should not be true for any v.")
end
end
--setup complete
return trivial, n, less
end
function sort_core.stable_sort(array, less)
--setup
local trivial, n, less = sort_core._sort_setup(array, less)
if not trivial then
--temp storage; allocate ahead of time
local workspace = {}
local middle = math.ceil(n / 2)
workspace[middle] = array[1]
--dive in
sort_core._merge_sort_impl( array, workspace, 1, n, less )
end
return array
end
function sort_core.insertion_sort(array, less)
--setup
local trivial, n, less = sort_core._sort_setup(array, less)
if not trivial then
sort_core._insertion_sort_impl(array, 1, n, less)
end
return array
end
sort_core.unstable_sort = table.sort
--export sort core to the global table module
function sort_core:export()
table.insertion_sort = sort_core.insertion_sort
table.stable_sort = sort_core.stable_sort
table.unstable_sort = sort_core.unstable_sort
end
return sort_core