csfrancis · July 6, 2014 19:57 · Jul 6, 2014
diff --git a/tsc_timer.lua b/tsc_timer.lua
@@ -0,0 +1,71 @@
+-- A timer that uses the rdtsc instruction to read the CPU timestamp counter.
+--
+-- Requires DynAsm with Lua mode: https://github.com/luapower/dynasm
+--
+-- Use it like this:
+--
+-- local tsc_timer = require('tsc_timer')
+-- local t = tsc_timer.start()
+-- ... do some things ...
+-- t:stop()
+-- print(t:value())
+--
+-- value() returns the estimated number of milliseconds and the number of ticks elapsed
+--
+local dynasm = require('dynasm')
+local ffi = require('ffi')
+
+local rdtsc = dynasm.loadstring [[
+local ffi = require('ffi')
+local dasm = require('dasm')
+
+|.arch x64
+|.actionlist actions
+
+local Dst = dasm.new(actions)
+| rdtsc
+| shl rdx, 32
+| or rax, rdx
+| ret
+
+local code = Dst:build()
+
+return function()
+  local _ = code
+  return ffi.cast('uint64_t __cdecl (*)()', code)()
+end
+]]()
+
+ffi.cdef [[
+int usleep(uint32_t usec);
+]]
+
+local _M = {}
+local mt = { __index = _M }
+
+function _M.initialize()
+  if _M.ticks_per_sec ~= nil then return end
+  local start_time = rdtsc()
+  ffi.C.usleep(200000)
+  local end_time = rdtsc() - start_time
+  _M.ticks_per_sec = end_time * 5
+end
+
+function _M.start()
+  if _M.ticks_per_second == nil then _M.initialize() end
+  return setmetatable({ start_time = rdtsc() }, mt)
+end
+
+function _M.stop(self)
+  local end_time = rdtsc()
+  if self.start_time == nil then error("timer has not been started") end
+  if self.stop_time ~= nil then error("timer has already been stopped") end
+  _M.end_time = end_time
+  return _M.value(self)
+end
+
+function _M.value(self)
+  return tonumber(self.end_time - self.start_time) / tonumber(self.ticks_per_sec) * 1000, tonumber(self.end_time - self.start_time)
+end
+
+return _M