>>501
もう見てないかも知れないが、
俺の古いPCで、64桁で0.4秒ほどの実行時間です

@echo off
setlocal enabledelayedexpansion
set "a=1234567890123456789012345678901234567890123456789012345678901234"
set "g=0123456789ABCDEF"
set "h="
set /a b=8,e=100000000
for /L %%i in (8,8,56) do if not "!a:~%%i,1!"=="" set /a b=%%i+8
set "a=0000000%a%"
set "a=!a:~-%b%!"
for /L %%i in (%b%,-8,8) do set /a "a%%i=1!a:~-%%i,8!-e"
:x
set /a c=0,f=0
for /L %%i in (%b%,-8,8) do set /a "d=a%%i+c*e,a%%i=d>>4,f|=a%%i,c=d&15"
set "h=!g:~%c%,1!%h%"
if %f% neq 0 goto x
for /f "delims=0 tokens=*" %%i in ("%h%") do set h=%%i
echo %h%
pause