Perf: Add a benchmark for the iconv FFI bindings

Certainly not the most representative workload, but it'll do.

Benchmarks/iconv-charset-conversion.lua

@@ -0,0 +1,74 @@
+local console = require("console")
+local iconv = require("iconv")
+local ffi = require("ffi")
+
+local SAMPLE_SIZE = 500000
+
+local function iconv_lowlevel()
+	local input = "\192\175\192\250\192\206\197\205\198\228\192\204\189\186"
+	local descriptor = iconv.bindings.iconv_open("UTF-8", "CP949")
+
+	local inputSize = ffi.new("size_t[1]", #input)
+	local inputBuffer = ffi.new("char[?]", #input, input)
+	local inputRef = ffi.new("char*[1]", inputBuffer)
+
+	local worstCaseOutputSize = #input * 4
+	local outputSize = ffi.new("size_t[1]", worstCaseOutputSize)
+	local outputBuffer = ffi.new("char[256]")
+	local outputRef = ffi.new("char*[1]", outputBuffer)
+
+	local result = iconv.bindings.iconv(descriptor, inputRef, inputSize, outputRef, outputSize)
+	local numConversionsPerformed = worstCaseOutputSize - outputSize[0]
+	local converted = ffi.string(outputBuffer, numConversionsPerformed)
+
+	iconv.bindings.iconv_close(descriptor)
+	return converted, result
+end
+
+local function iconv_lua()
+	local input = "\192\175\192\250\192\206\197\205\198\228\192\204\189\186"
+	local output, message = iconv.convert(input, "CP949", "UTF-8")
+	return output, message
+end
+
+local function iconv_cpp()
+	local inputBuffer = buffer.new()
+	local outputBuffer = buffer.new(1024)
+	local ptr, len = outputBuffer:reserve(1024)
+	local result = iconv.bindings.iconv_convert(inputBuffer, #inputBuffer, "CP949", "UTF-8", ptr, len)
+	return result
+end
+
+math.randomseed(os.clock())
+local availableBenchmarks = {
+	function()
+		local label = "[FFI] Low-level API (tedious and slow, but the most flexible)"
+		console.startTimer(label)
+		for i = 1, SAMPLE_SIZE, 1 do
+			iconv_lowlevel()
+		end
+		console.stopTimer(label)
+	end,
+	function()
+		local label = "[FFI] One-shot C++ conversion (fast but less flexible)"
+		console.startTimer(label)
+		for i = 1, SAMPLE_SIZE, 1 do
+			iconv_cpp()
+		end
+		console.stopTimer(label)
+	end,
+	function()
+		local label = "[FFI] Lua-friendly wrapper (safer, but slower)"
+		console.startTimer(label)
+		for i = 1, SAMPLE_SIZE, 1 do
+			iconv_lua()
+		end
+		console.stopTimer(label)
+	end,
+}
+
+table.shuffle(availableBenchmarks)
+
+for _, benchmark in ipairs(availableBenchmarks) do
+	benchmark()
+end