String converter between Windows ANSI and UTF-8 encodings

win-125x.lua

---------------------------------------------------------------------
-- Converter between win-125x and UTF-8 strings
---------------------------------------------------------------------
-- Written in pure Lua, compatible with Lua 5.1-5.4
-- Usage example:
--    require("win-125x")
--    str_win  = utf8_to_win(str_utf8)
--    str_utf8 = win_to_utf8(str_win)
---------------------------------------------------------------------

local codepage = 1251   -- Set your codepage here

-- The following codepages are supported:
--   874  Thai
--  1250  Central European
--  1251  Cyrillic
--  1252  Western
--  1253  Greek
--  1254  Turkish
--  1255  Hebrew
--  1256  Arabic
--  1257  Baltic
--  1258  Vietnamese

do
   local compressed_mappings = {
      -- Unicode to win-125x mappings are taken from unicode.org, compressed and protected by a checksum
      [874]  =  -- Thai, 97 codepoints above U+007F
         [[!%l+$"""WN^9=&$pqF'oheO#;0l#"hs)mI[=e!ufwkDB#OwLnJ|IRIUz8Q(MMM]],
      [1250] =  -- Central European, 123 codepoints above U+007F
         [[!<2#?v"1(ro;xh/tL_3hC^i;e~PjO"p<I\aTT};]Rb~M7/]&jRjfwuE%AJ)@XfBQy&\jy[V5:]!RtH]m>Yd8m?6LpsUA\V=x'VcMO<Wz+EOO
         0m7U`u|$Y5x?Vk*6+qJ@/0Lie77_b}OEuwv$Qj/w`+J>M*<g2qxD3qEyC&*{VGI'UddQ`GQ)L=lj<{S;Jm),f3yzcQOuxacHSZ{X'XIWzDz!?E
         =U0f]],
      [1251] =  -- Cyrillic, 127 codepoints above U+007F
         [[!-[;_8kMai7j]xB$^n)#7ngrX}_b%{<Cdot;P?2J&00&^wX|;]@N*fjq#ioX'v.&gG@ur~3yi8t1;xn40{G#NX?7+hGC{$D"4#oJ//~kflzs
         "_\z9qP#}1o|@{t`2NrM%t{MW?X9d6o:MqHl6+z]],
      [1252] =  -- Western, 123 codepoints above U+007F
         [[!)W$<c~\OdA5TJ%/J/{:yoE]K[d,c<Mv+gp_[_UuB52c;H&{leFk%Kd8%cHnvLrB[>|:)t.}QH*)]AD|LqjsB+JCdKmbRIjO,]],
      [1253] =  -- Greek, 111 codepoints above U+007F
         [[!./yDCq;#WAuC\C1R{=[n'FpSuc!"R\EZ|4&J?A3-z?*TI?ufbhFq1J!x@Sjff\!G{o^dDXl|8NLZ!$d'8$f^=hh_DPm!<>>bCgV(>erUWhX
         ?R+-JP@4ju:Yw#*C]],
      [1254] =  -- Turkish, 121 codepoints above U+007F
         [[!-(R[SPKY>cgcK5cCs4vk%MuL`yFx^Bl#/!l#M@#yoe|Jx+pxZuvh%r>O</n_gb>hDjmG]j#lA{]2"R-Z@(6Wy:Q~%;327b&fRSkF#BM/d+%
         iWmSx4E*\F_z=s>QeJBqC^]],
      [1255] =  -- Hebrew, 105 codepoints above U+007F
         [[!.b\.H?S\21+7efm'`w&MW_Jg,mRbB;{X@T\3::DC#7<m_cAE!:%C%c7/,./u[8w*h-iwpz03QY,ay%]MI*D]W&]UG^3(=20a7$zG[Ng7MLt
         sXIne(V37A?OO%|Hn13wMh-?^jNzhW`,-]],
      [1256] =  -- Arabic, 128 codepoints above U+007F
         [[!3n8GE$.to/ka%Nx`uOpcib>|9KU-N72!1J4c2NAUE3a,HlOE=M`@rsa||Nh_!og]:dILz9KNlF~vigNH*a0KxwjjfR*]?tO87(a3-RQex^V
         Ww&SY{:AqE|s%}@U8%rKcr0,NCjR:N&L'YyGu<us'sN*1pl=gAXOwSJ[v?f;imBhDu_)d$F8T?%S[]],
      [1257] =  -- Baltic, 116 codepoints above U+007F
         [[!:<_.XQ[;n35s%I?g9)b/7DiGwIR)zy&=6?/3)6iO%rSnC_6yjl'8#zeN0vcW_yX/2*J93+EJVrW,^Rhe,h7wWl"}neF2~F[PyD;BcrG*5=J
         fh<x!FJ?qSw9Xp!;WB3T<J^x?#Ie`xufezR'\I(eED]3d&)VJL$/+$Zf;W^I>L[3D5F<_IcGpn=oX"JR1%arS|FX|dia4]BeF>d5p`EV+:;*I<
         x^Voq{"f]],
      [1258] =  -- Vietnamese, 119 codepoints above U+007F
         [[!3n8C{%C0}&p3gE0~|&RVm9Wr&^ln1}'$gV{bml1oByN*bb:Bm^E;~B3-WjF6Qubq^`Y*6\0^w!DKpK<\7lHVELmSXN{2~B"0C"<1CYN2{$a
         5M?>|7%~qm{pXphwm3$}iyXjBYwtGqxp(f[!g^Ee9H.}1~0H-k-dzNDh1L]],
   }
   local char, byte, gmatch, floor, string_reverse = string.char, string.byte, string.gmatch, math.floor, string.reverse
   local table_insert, table_concat = table.insert, table.concat

   local function decompress_mapping()
      local width, offset, base, CS1, CS2, get_next_char = 1.0, 0.0, 0.0, 7^18, 5^22, gmatch(compressed_mappings[codepage], "%S")
      local mapping, rev_mapping, trees, unicode, ansi, prev_delta_unicode, prev_delta_ansi = {}, {}, {}, 0x7F, 0x7F

      local function decompress_selection(qty, tree)
         while width <= 94^7 do
            width, offset, base = width * 94.0, offset * 94.0 + byte(get_next_char()) - 33.0, (base - floor((base + width - 1) / 94^7) * 94^7) * 94.0
         end
         if qty then
            local big_qty = width % qty
            local small_unit = (width - big_qty) / qty
            local big_unit = small_unit + 1.0
            local offset_small = big_qty * big_unit
            local from, offset_from, left, right
            if offset < offset_small then
               width = big_unit
               offset_from = offset - offset % big_unit
               from = offset_from / big_unit
            else
               width = small_unit
               offset_from = offset - (offset - offset_small) % small_unit
               from = big_qty + (offset_from - offset_small) / small_unit
            end
            local len, leaf = 1.0, from
            if tree then
               leaf, left, right = 4, 0, qty
               repeat
                  local middle = tree[leaf]
                  if from < middle then
                     right = middle
                  else
                     left, leaf = middle, leaf + 1
                  end
                  leaf = tree[leaf + 1]
               until leaf < 0
               from, len = left, right - left
               offset_from = left < big_qty and left * big_unit or offset_small + (left - big_qty) * small_unit
               width = (right < big_qty and right * big_unit or offset_small + (right - big_qty) * small_unit) - offset_from
            end
            base, offset = base + offset_from, offset - offset_from
            CS1, CS2 = (CS1 % 93471801.0) * (CS2 % 93471811.0) + qty, (CS1 % 93471821.0) * (CS2 % 93471831.0) - from * 773.0 - len * 7789.0
            return leaf
         end
         assert((CS1 - CS2) % width == offset)
      end

      local function get_delta(tree_idx)
         local tree = trees[tree_idx]
         local val = tree[3]
         if val == 0.0 then
            local leaf = decompress_selection(tree[1], tree)
            local max_exp_cnt = tree[2]
            val = leaf % max_exp_cnt
            leaf = (leaf - val) / max_exp_cnt + 2.0
            val = 2.0^val
            val = val + decompress_selection(val)
            if leaf ~= 0.0 then
               return leaf * val
            end
         end
         tree[3] = val - 1.0
      end

      for tree_idx = 1, 2 do
         local total_freq = decompress_selection(2^15)
         local max_exp_cnt = decompress_selection(17)
         local tree, qty_for_leaf_info = {total_freq, max_exp_cnt, 0.0}, 3 * max_exp_cnt

         local function build_subtree(left, right, idx)
            local middle, subtree = left + 1
            middle = decompress_selection(right - middle) + middle
            tree[idx], idx = middle, idx + 3
            for next_idx = idx - 2, idx - 1 do
               if decompress_selection(2) == 1 then
                  subtree, idx = idx, build_subtree(left, middle, idx)
               else
                  subtree = decompress_selection(qty_for_leaf_info) - qty_for_leaf_info
               end
               tree[next_idx], left, middle = subtree, middle, right
            end
            return idx
         end

         build_subtree(0, total_freq, 4)
         trees[tree_idx] = tree
      end
      while true do
         local delta = get_delta(1)
         if not delta then
            delta = prev_delta_unicode
         elseif delta == prev_delta_unicode then
            decompress_selection()
            return mapping, rev_mapping
         end
         unicode, prev_delta_unicode, delta = unicode + delta, delta, get_delta(2) or prev_delta_ansi
         ansi, prev_delta_ansi = ansi + delta, delta
         mapping[unicode] = ansi
         rev_mapping[ansi] = unicode
      end
   end

   local map_unicode_to_ansi, map_ansi_to_unicode = decompress_mapping()

   function utf8_to_win(str)
      local result_ansi = {}
      for u in gmatch(str, ".[\128-\191]*") do
         local code = byte(u)%2^(8-#u)
         for j = 2, #u do
            code = (code-2)*64+byte(u,j)
         end
         table_insert(result_ansi, char(code < 128 and code or map_unicode_to_ansi[code] or byte"?"))
      end
      return table_concat(result_ansi)
   end

   function win_to_utf8(str)
      local result_utf8 = {}
      for pos = #str, 1, -1 do
         local code, h = byte(str, pos), 127
         code = code < 128 and code or map_ansi_to_unicode[code] or byte"?"
         while code > h do
            table_insert(result_utf8, char(128 + code%64))
            code, h = floor(code/64), 288067%h
         end
         table_insert(result_utf8, char((127-h)*2+code))
      end
      return string_reverse(table_concat(result_utf8))
   end

end

hello congrats for the good job!
I have to mention that for french some characters are wrongly converted ex: é / è /à /.. these are really important to display a correct french.
Is there a way to rectify this?
Thank u again.

hello congrats for the good job! I have to mention that for french some characters are wrongly converted ex: é / è /à /.. these are really important to display a correct french. Is there a way to rectify this? Thank u again.

Please show the example of wrong conversion:

1. the value of variable codepage at line #11
2. the function you are using (utf8_to_win or win_to_utf8)
3. the sequence of bytes in input and output strings as displayed by print(str_win:byte(1,-1));print(str_utf8:byte(1,-1))
4. the result of conversion you expect
5. the ANSI codepage of your OS (open cmd.exe, type reg query HKLM\SYSTEM\CurrentControlSet\Control\Nls\CodePage /v ACP and look for the number after the word REG_SZ)

Hello and thank you for the prompt reply:
1- Used codepage =1252
2- function: utf8_to_win(str)
3- Bytes sequence (I hope I got the question right)
'Météo' >> 77 195 131 194 169 116 195 131 194 169 111
4- _Here are few words with their expected results:
'Tiliachat' >> 'Téléachat'
'Frangais' >> 'Français'
'dhs' >> 'dès'
'mjme' >> 'même'
5- ANSI codepage of my OS: 1252
Best regards.

For the string "Météo" it correctly replaces UTF8 "\195\131" with win1252 "\195"
For the string "Téléachat" it correctly replaces UTF8 "\195\169" with win1252 "\233"

local str_utf8 = "Téléachat"
assert(str_utf8 == "\84\195\169\108\195\169\97\99\104\97\116")
local str_win = utf8_to_win(str_utf8)
assert(str_win == "\84\233\108\233\97\99\104\97\116")

Probably, the problem is how the string is displayed on your side.
For example, to view correct win-1252 symbols in Windows command line (cmd.exe) you need to invoke chcp 1252 before running your program.
Please show a screenshot.

Shot from my Grid where 'é' is shown as 'i' (the words I mentioned above are also extracted from the same grid).
I tried all languages and they perfectly work. Only french is making these troubles for me.

'Probably, the problem is how the string is displayed on your side.'
Yes Sir! I tried it on two other pc and the module is just perfect. All characters are showing right ! I don't know what is goin' on with the one I've got these troubles on.
I really do appreciate your help and the good advise.
Congrats again.
Thank you very much and good weekend Sir.

So the tool would only work with the characters that correspond with the local machine's codepage, right?

@movalex - Yes, characters must be from your 1-byte Windows ANSI codepage.

Thank you!