diff --git a/src/create_cmdidxs.vim b/src/create_cmdidxs.vim
new file mode 100644
index 0000000..c306ccb
--- /dev/null
+++ b/src/create_cmdidxs.vim
@@ -0,0 +1,81 @@
+" This script generates the tables cmdidxs1[] and cmdidxs2[][] which,
+" given a Ex command, determine the first value to probe to find
+" a matching command in cmdnames[] based on the first character
+" and the first 2 characters of the command.
+" This is used to speed up lookup in cmdnames[].
+"
+" Script should be run every time new Ex commands are added in Vim,
+" from the src/vim directory, since it reads commands from "ex_cmds.h".
+
+let cmds = []
+let skipped_cmds = 0
+
+for line in readfile('ex_cmds.h')
+  if line =~ '^EX(CMD_'
+    let m = matchlist(line, '^EX(CMD_\S*,\s*"\([a-z][^"]*\)"')
+    if len(m) >= 2
+      let cmds += [ m[1] ]
+    else
+      let skipped_cmds += 1
+    endif
+  endif
+endfor
+
+let cmdidxs1 = {}
+let cmdidxs2 = {}
+
+for i in range(len(cmds) - 1, 0, -1)
+  let cmd = cmds[i]
+  let c1 = cmd[0] " First character of command
+  let c2 = cmd[1] " Second character of command (if any)
+
+  let cmdidxs1{c1} = i
+  if c2 >= 'a' && c2 <= 'z'
+    let cmdidxs2{c1}{c2} = i
+  endif
+endfor
+
+let output =  [ '/* Automatically generated code by create_cmdidxs.vim' ]
+let output += [ ' *' ]
+let output += [ ' * Table giving the index of the first command in cmdnames[] to lookup' ]
+let output += [ ' * based on the first letter of a command.' ]
+let output += [ ' */' ]
+let output += [ 'static const unsigned short cmdidxs1[26] =' ]
+let output += [ '{' ]
+
+let a_to_z = map(range(char2nr('a'), char2nr('z')), 'nr2char(v:val)')
+for c1 in a_to_z
+  let line = '  /* ' . c1 . ' */ ' . cmdidxs1{c1} . ((c1 == 'z') ? '' : ',')
+  let output += [ line ]
+endfor
+let output += [ '};' ]
+let output += [ '' ]
+let output += [ '/*' ]
+let output += [ ' * Table giving the index of the first command in cmdnames[] to lookup' ]
+let output += [ ' * based on the first 2 letters of a command.' ]
+let output += [ ' * Values in cmdidxs2[c1][c2] are relative to cmdidxs1[c1] so that they' ]
+let output += [ ' * fit in a byte.' ]
+let output += [ ' */' ]
+let output += [ 'static const unsigned char cmdidxs2[26][26] =' ]
+let output += [ '{ /*         a   b   c   d   e   f   g   h   i   j   k   l   m   n   o   p   q   r   s   t   u   v   w   x   y   z */' ]
+
+for c1 in a_to_z
+  let line = '  /* ' . c1 . ' */ {'
+  for c2 in a_to_z
+    if exists('cmdidxs2{c1}{c2}')
+      let line .= printf('%3d', cmdidxs2{c1}{c2} - cmdidxs1{c1})
+    else
+      let line .= '  0'
+    endif
+    let line .= (c2 == 'z') ? '' : ','
+  endfor
+  let line .= ' }' . ((c1 == 'z') ? '' : ',')
+  let output += [ line ]
+endfor
+
+let output += [ '};' ]
+let output += [ '' ]
+let output += [ 'static const int command_count = ' . (len(cmds) + skipped_cmds) . ';' ]
+
+call writefile(output, "ex_cmdidxs.h")
+quit