-- Shared timing helpers for the wall-clock benchmark runners.

--

-- os.clock() measures CPU time, not wall time. For these CPU-bound loops

-- that is the right metric (time the process spends scheduled out does not

-- pollute samples), but it would silently under-report anything I/O-bound.

-- luacheck: read globals jit

local M = {}

-- Runs fn(n) once untimed (lets LuaJIT compile traces: a loop becomes a

-- tracing candidate after 56 iterations, a side exit after 10), then times

-- `samples` runs with the collector stopped, starting each sample from a

-- freshly collected heap. Reports the median so a stray outlier sample

-- cannot move the headline number.

function M.measure(fn, n, samples)

samples = samples or 5

assert(samples >= 1, "samples must be >= 1")

local checksum = fn(n)

local times = {}

for s = 1, samples do

collectgarbage("collect")

collectgarbage("stop")

local t0 = os.clock()

fn(n)

local t1 = os.clock()

collectgarbage("restart")

times[s] = t1 - t0

end

table.sort(times)

local mid = math.floor((#times + 1) / 2)

local median = times[mid]

if #times % 2 == 0 then

median = (times[mid] + times[mid + 1]) / 2

end

return {

median = median,

min = times[1],

max = times[#times],

checksum = checksum,

}

end

function M.runtime_tag()

if jit then

return jit.status() and "luajit" or "luajit-joff"

end

return (_VERSION:gsub("%s", ""):lower())

end

function M.report(bench_name, variant_name, n, r)

io.write(string.format(

"%-13s %-8s %-12s n=%-9.0f median=%8.4fs min=%8.4fs max=%8.4fs result=%s\n",

bench_name,

variant_name,

M.runtime_tag(),

n,

r.median,

r.min,

r.max,

tostring(r.checksum)

))

end

return M