[wip] lua port of benchmark-ips

Warming up --------------------------------------
                 ffi
    708409 i/100ms

             syscall
    593019 i/100ms

Calculating -------------------------------------
 11385724.4 (±1.9%) i/s -   57381129 in   5.041731s
 10427682.8 (±1.0%) i/s -   52185672 in   5.005021s

benchmark/ips.lua

@@ -0,0 +1,379 @@
+local function to_i(str) return tonumber(str:gsub('[^%d]', ''), 10) end
+
+local NANOSECONDS_PER_SECOND = to_i('1 000 000 000')
+local NANOSECONDS_PER_100MS = to_i('100 000 000')
+local Timing = { }
+
+
+local ffi = require 'ffi'
+
+ffi.cdef [[
+typedef int clockid_t;
+typedef long time_t;
+
+struct timespec {
+  time_t tv_sec;
+  long tv_nsec;
+};
+
+int clock_gettime(clockid_t clk_id, struct timespec *tp);
+]]
+
+
+local CLOCK = {
+  REALTIME                  = 0,
+  MONOTONIC                 = 1,
+  PROCESS_CPUTIME_ID        = 2,
+  THREAD_CPUTIME_ID         = 3,
+  MONOTONIC_RAW             = 4,
+  REALTIME_COARSE           = 5,
+  MONOTONIC_COARSE          = 6,
+}
+
+local ts = ffi.new("struct timespec[1]")
+
+-- Get an object that represents now in nanoseconds
+function Timing.now()
+  assert(ffi.C.clock_gettime(clock or CLOCK.MONOTONIC_RAW, ts) == 0,
+    "clock_gettime() failed: "..ffi.errno())
+  return tonumber(ts[0].tv_sec * 1e9 + ts[0].tv_nsec)
+end
+
+-- Recycle used objects by starting Garbage Collector.
+function Timing.clean_env()
+  collectgarbage('collect')
+end
+
+-- Return the number of microseconds between the 2 moments
+function Timing.time_ns(before, after)
+  return after - before
+end
+
+-- Add one second to the time represenetation
+function Timing.add_second(t, s)
+  return t + (s * NANOSECONDS_PER_SECOND)
+end
+
+
+local Report = {}
+local ReportEntry = {}
+local Entry = {}
+local Stats = {}
+
+local function _just(str, width, char)
+  local delta = width - #str
+
+  if delta > 0 then
+    return (char or ' '):rep(delta)
+  else
+    return ''
+  end
+end
+
+local function rjust(str, width, char)
+  return _just(str, width, char) .. str
+end
+
+local function ljust(str, width, char)
+  return str .. _just(str, width, char)
+end
+
+-- Add padding to label's right if label's length < 20, Otherwise add a new line and 20 whitespaces.
+local function rjust_label(label)
+  local delta = 20 - #label
+
+  if delta > 0 then
+    return rjust(label, 20)
+  else
+    return label .. "\n" .. rjust('', 20)
+  end
+end
+
+local IPS = {
+  time = 5,
+  warmup = 2,
+  iterations = 1,
+  hooks = {
+    start_warming = {
+      function() print('Warming up --------------------------------------') end,
+    },
+    warming = {
+      function(label) print(rjust_label(label)) end,
+    },
+    warmup_stats = {
+      function(_, timing) print(("%10d i/100ms\n"):format(timing)) end,
+    },
+
+    start_running = {
+      function() print('Calculating -------------------------------------') end,
+    },
+    running = {},
+    report_entry = {
+      function(report) print(" ", report:body()) end,
+    },
+
+    done = {},
+  },
+}
+
+
+local IPS_mt = {
+  __index = IPS,
+  __newindex = function(_, k) error("unknown property: " .. k) end,
+}
+
+function IPS:call(f)
+  local ips = self:new()
+
+  f(ips)
+  ips:run()
+
+  return
+end
+
+function IPS:new()
+  local m = {
+    time = self.time,
+    warmup = self.warmup,
+    iterations = self.iterations,
+    full_report = Report:new(),
+    items = {}, timing = {},
+    hooks = self.hooks,
+  }
+
+  return setmetatable(m, IPS_mt)
+end
+
+function IPS:notify(name, ...)
+  for _, fun in ipairs(self.hooks[name]) do
+    fun(...)
+  end
+end
+
+function IPS:report(label, fun)
+  table.insert(self.items, Entry:new(label, fun))
+end
+
+function IPS:compare()
+  if #self.items < 1 then
+    error("no items to test")
+  end
+end
+
+
+local floor = math.floor
+
+-- Calculate the cycles needed to run for approx 100ms,
+-- given the number of iterations to run the given time.
+-- @tparam Float time_nsec Each iteration's time in ns.
+-- @tparam Integer iters Iterations.
+-- @treturn Integer Cycles per 100ms.
+
+local function cycles_per_100ms(time_nsec, iters)
+  cycles = floor((NANOSECONDS_PER_100MS / time_nsec) * iters)
+  if cycles <= 0 then return 1 else return cycles end
+end
+
+-- Calculate the interations per second given the number
+-- of cycles run and the time in microseconds that elapsed.
+-- @tparam Integer cycles Cycles.
+-- @tparam Integer time_ns Time in microsecond.
+-- @treturn Float Iteration per second.
+local function iterations_per_sec(cycles, time_ns)
+  return NANOSECONDS_PER_SECOND * (cycles / time_ns)
+end
+
+function IPS:run_warmup()
+  for _,item in ipairs(self.items) do
+
+    self:notify('warming', item.label, self.warmup)
+
+    Timing:clean_env()
+
+    local before = Timing.now()
+    local target = Timing.add_second(before, self.warmup)
+
+    warmup_iter = 0
+
+    while Timing.now() < target do
+      item:call_times(1)
+      warmup_iter = warmup_iter + 1
+    end
+
+    after = Timing.now()
+    warmup_time_ns = Timing.time_ns(before, after)
+
+    self.timing[item] = cycles_per_100ms(warmup_time_ns, warmup_iter)
+
+    self:notify('warmup_stats', warmup_time_ns, self.timing[item])
+  end
+end
+
+local insert = table.insert
+
+local sum = function(t)
+  local total = 0
+  for _, n in ipairs(t) do
+    total = total + n
+  end
+  return total
+end
+
+local map = function(t, f)
+  local m = {}
+
+  for i, n in ipairs(t) do
+    m[i] = f(n)
+  end
+
+  return m
+end
+
+function IPS:run_benchmark()
+  for _,item in ipairs(self.items) do
+    self:notify('running', item.label, self.time)
+
+    Timing:clean_env()
+
+
+    local iter = 0
+    local measurements_ns = {}
+
+    -- Running this number of cycles should take around 100ms.
+    local cycles = self.timing[item]
+
+    local after
+    local before = Timing.now()
+    local target = Timing.add_second(before, self.time)
+
+    while before < target do
+      item:call_times(cycles)
+      after = Timing.now()
+
+      -- If for some reason the timing said this took no time (O_o)
+      -- then error out.
+      local iter_ns = Timing.time_ns(before, after)
+
+      if iter_ns <= 0 then
+        error('impossible happened')
+      end
+
+      before = after
+
+      iter = iter + cycles
+      insert(measurements_ns, iter_ns)
+    end
+
+    local final_time = after
+    local measured_ns = sum(measurements_ns)
+    local samples = map(measurements_ns, function(time_ns) return iterations_per_sec(cycles, time_ns) end)
+
+    local rep = self.full_report:add_entry(item.label, measured_ns, iter, Stats:new(samples), cycles)
+
+    self:notify('report_entry', rep)
+  end
+end
+
+function IPS:run()
+  if self.warmup and self.warmup > 0 then
+    for i=1, self.iterations do
+      self:notify('start_warming')
+      self:run_warmup()
+    end
+  end
+
+  self:notify('start_running')
+
+  for i=1, self.iterations do
+    self:run_benchmark()
+  end
+
+  self:notify('done')
+end
+
+function Entry:new(label, action)
+  local entry = { label = label, action = action }
+  return setmetatable(entry, { __index = self })
+end
+
+function Entry:call_times(n)
+  local action = self.action
+
+  for i=1, n do
+    action()
+  end
+end
+
+function Report:new()
+  return setmetatable({
+    entries = {},
+  }, { __index = self })
+end
+
+function Report:add_entry(label, nanoseconds, iters, stats, measurement_cycle)
+  local entry = ReportEntry:new(label, nanoseconds, iters, stats, measurement_cycle)
+
+  table.insert(self.entries, entry)
+
+  return entry
+end
+
+function Report:body(format)
+  local left = ("%s (±%4.1f%%) i/s"):format()
+end
+
+function ReportEntry:new(label, nanoseconds, iterations, stats, measurement_cycle)
+  return setmetatable({
+    label = label,
+    nanoseconds = nanoseconds,
+    iterations = iterations,
+    stats = stats,
+    measurement_cycle = measurement_cycle,
+  }, { __index = self })
+end
+
+function ReportEntry:error_percentage()
+  return 100.0 * (self.stats.error / self.stats.central_tendency)
+end
+
+function ReportEntry:body()
+  local left = ("%10.1f (±%.1f%%) i/s"):format(self.stats.central_tendency, self:error_percentage())
+
+  return ljust(left, 20) .. (" - %10d in %10.6fs"):format(self.iterations, self:runtime())
+end
+
+function ReportEntry:runtime()
+  return self.nanoseconds / NANOSECONDS_PER_SECOND
+end
+
+local function stat_mean(samples)
+  local sum = sum(samples)
+  return sum / #samples
+end
+
+local function stat_variance(samples, m)
+  local mean = m or stat_mean(samples)
+  local total = sum(map(samples, function(n) return math.pow(n - mean, 2) end))
+
+  return total / #samples
+end
+
+local function stat_stddev(samples, m)
+  return math.sqrt(stat_variance(samples, m))
+end
+
+function Stats:new(samples)
+  local mean = stat_mean(samples)
+  local error = stat_stddev(samples, mean)
+
+  return setmetatable({
+    central_tendency = mean,
+    error = error,
+  }, { __index = self })
+end
+
+
+return setmetatable(IPS, {
+  __call = function(_, f) return IPS:call(f) end,
+  __newindex = IPS_mt.__newindex,
+})