compare shifting up and down

compare_shifts.jl

function shiftup(v::AbstractVector{T}, start, finish) where {T}
    for i in finish:-1:start
        @inbounds v[i+1] = v[i]
    end
end

function shiftup4(v::AbstractVector{T}, start, finish) where {T}
    n = finish - start
    q, r = fldmod(n, 4)
    @inbounds for i in finish-3:-4:start+r
        v[i+4] = v[i+3]
        v[i+3] = v[i+2]
        v[i+2] = v[i+1]
        v[i+1] = v[i]
    end
    if !iszero(r)
        @inbounds for i in start+r:-1:start
            v[i+1] = v[i]
        end
    end
end

"""
    shiftdown(v, start>1, finish<=length(v))

shift contents of Vector from start through finish down by 1 position
"""
function shiftdown(v::AbstractVector{T}, start, finish) where {T}
    for i in start:finish
        @inbounds v[i-1] = v[i]
    end
end

function shiftdown4(v::AbstractVector{T}, start, finish) where {T}
    n = finish - start
    q, r = fldmod(n, 4)
    @inbounds for i in start:4:finish-r
        v[i-1] = v[i]
        v[i] = v[i+1]
        v[i+1] = v[i+2]
        v[i+2] = v[i+3]
    end
    if !iszero(r)
        @inbounds for i in finish-r:finish
            @inbounds v[i+1] = v[i]
        end
    end
end

using BenchmarkTools

v = sort(rand(10:990, 2048));
v1 = deepcopy(v);
v2 = deepcopy(v);
v3 = deepcopy(v);
v4 = deepcopy(v);

start = 1000;
finish = start + 250;

v1t = @belapsed shiftup($v1, $start, $finish);
v2t = @belapsed shiftup4($v2, $start, $finish);

v3t = @belapsed shiftdown($v3, $start, $finish);
v4t = @belapsed shiftdown4($v4, $start, $finish);

inanos(t) = round(Int, t * 1_000_000_000);

t1 = inanos(v1t);
t2 = inanos(v2t);
t3 = inanos(v3t);
t4 = inanos(v4t);

ups = (shiftup=t1, shiftup4=t2)
downs = (shiftdown=t3, shiftdown4=t4)

ratios = round.(Tuple(ups) .// Tuple(downs), sigdigits=2)

#=


julia> ups = (shiftup=t1, shiftup4=t2)
(shiftup = 62, shiftup4 = 30)

julia> downs = (shiftdown=t3, shiftdown4=t4)
(shiftdown = 18, shiftdown4 = 21)

julia>

julia> ratios = round.(Tuple(ups) .// Tuple(downs), sigdigits=2)
(3.4, 1.4)

=#