base64decode.asp

一个不错的个人商务网站的源码

<%
const BASE_64_MAP_INIT ="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

     ' zero based arrays

     dim Base64EncMap(63)

     dim Base64DecMap(127)

     PUBLIC SUB initCodecs()
          ' setup base 64

          dim max, idx

             max = len(BASE_64_MAP_INIT)

          for idx = 0 to max - 1

               ' one based string

               Base64EncMap(idx) = mid(BASE_64_MAP_INIT, idx + 1, 1)

          next

          for idx = 0 to max - 1

               Base64DecMap(ASC(Base64EncMap(idx))) = idx

          next

     END SUB

     ' decode base 64 encoded string

     PUBLIC FUNCTION base64Decode(scrambled)



          if len(scrambled) = 0 then

               base64Decode = ""

               exit function

          end if



          ' ignore padding

          dim realLen

          realLen = len(scrambled)

          do while mid(scrambled, realLen, 1) = "="

               realLen = realLen - 1

          loop

          dim ret, ndx, by4, first, second, third, fourth

          ret = ""

          by4 = (realLen \ 4) * 4

          ndx = 1

          do while ndx <= by4

               first  = Base64DecMap(asc(mid(scrambled, ndx+0, 1)))

               second = Base64DecMap(asc(mid(scrambled, ndx+1, 1)))

               third  = Base64DecMap(asc(mid(scrambled, ndx+2, 1)))

               fourth = Base64DecMap(asc(mid(scrambled, ndx+3, 1)))

               ret = ret & chr( ((first * 4) AND 255) +   ((second \ 16) AND 3))

               ret = ret & chr( ((second * 16) AND 255) + ((third \ 4) AND 15) )

               ret = ret & chr( ((third * 64) AND 255) +  (fourth AND 63) )

               ndx = ndx + 4

          loop

          ' check for stragglers, will be 2 or 3 characters

          if ndx < realLen then

               first  = Base64DecMap(asc(mid(scrambled, ndx+0, 1)))

               second = Base64DecMap(asc(mid(scrambled, ndx+1, 1)))

               ret = ret & chr( ((first * 4) AND 255) +   ((second \ 16) AND 3))

               if realLen MOD 4 = 3 then

                    third = Base64DecMap(asc(mid(scrambled,ndx+2,1)))

                    ret = ret & chr( ((second * 16) AND 255) + ((third \ 4) AND 15) )

               end if

          end if



          base64Decode = ret

     END FUNCTION
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