diff --git a/bench/get_line.lua b/bench/get_line.lua
new file mode 100644
index 0000000..bf74e91
--- /dev/null
+++ b/bench/get_line.lua
@@ -0,0 +1,49 @@
+local ffi = require('ffi')
+local api = vim.api
+
+-- FFI definition for ml_get
+ffi.cdef([[
+  typedef int32_t linenr_T;
+  char *ml_get(linenr_T lnum);
+]])
+
+local C = ffi.C
+
+-- Function to get line using ml_get
+local function get_line_with_ml_get(lnum)
+  return ffi.string(C.ml_get(lnum))
+end
+
+-- Function to get line using api.nvim_buf_get_lines
+local function get_line_with_api(bufnr, lnum)
+  return api.nvim_buf_get_lines(bufnr, lnum - 1, lnum, false)[1]
+end
+
+-- Benchmark function
+local function benchmark(func, bufnr, lnum, iterations)
+  local start_time = vim.uv.hrtime()
+  for _ = 1, iterations do
+    func(bufnr, lnum)
+  end
+  local end_time = vim.uv.hrtime()
+  return (end_time - start_time) / iterations
+end
+
+-- Example usage
+local bufnr = api.nvim_get_current_buf()
+vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, { ('text '):rep(100) })
+local lnum = 1
+local iterations = 10000
+
+-- Warm up
+get_line_with_ml_get(lnum)
+get_line_with_api(bufnr, lnum)
+
+-- Run benchmarks
+local time_ml_get = benchmark(function(_, lnum)
+  return get_line_with_ml_get(lnum)
+end, bufnr, lnum, iterations)
+local time_api = benchmark(get_line_with_api, bufnr, lnum, iterations)
+
+print(string.format('ml_get: %.3f ns per call', time_ml_get))
+print(string.format('api.nvim_buf_get_lines: %.3f ns per call', time_api))
diff --git a/bench/space_or_tab.lua b/bench/space_or_tab.lua
index b23351c..de791d2 100644
--- a/bench/space_or_tab.lua
+++ b/bench/space_or_tab.lua
@@ -1,7 +1,7 @@
 local function only_spaces_or_tabs(text)
   for i = 1, #text do
-    local c = text:sub(i, i)
-    if c ~= ' ' and c ~= '\t' then
+    local byte = string.byte(text, i)
+    if byte ~= 32 and byte ~= 9 then -- 32 is space, 9 is tab
       return false
     end
   end
@@ -30,5 +30,5 @@ local time2 = benchmark(only_spaces_or_tabs_regex, text, iterations)
 print('Time for only_spaces_or_tabs:', time1)
 print('Time for only_spaces_or_tabs_regex:', time2)
 
--- Time for only_spaces_or_tabs: 0.07258
--- Time for only_spaces_or_tabs_regex: 0.093389
+-- Time for only_spaces_or_tabs: 0.027799
+-- Time for only_spaces_or_tabs_regex: 0.093943
diff --git a/lua/indentmini/init.lua b/lua/indentmini/init.lua
index 8f13b90..6f049b1 100644
--- a/lua/indentmini/init.lua
+++ b/lua/indentmini/init.lua
@@ -43,8 +43,8 @@ local context = { snapshot = {} }
 --- @return boolean true only have space or tab
 local function only_spaces_or_tabs(text)
   for i = 1, #text do
-    local c = text:sub(i, i)
-    if c ~= ' ' and c ~= '\t' then
+    local byte = string.byte(text, i)
+    if byte ~= 32 and byte ~= 9 then -- 32 is space, 9 is tab
       return false
     end
   end