Implements an encoder using a table-driven alphabet to produce output represented in the US-ASCII character set.
TIdEncoder3to4 = class(TIdEncoder);
TIdEncoder3to4 is a TIdEncoder descendant that provides encoding capabilities that represents arbitrary sequences of byte data in a form that need not be humanly readable.
TIdEncoder3to4 is almost identical to the mechanism used in Privacy Enhanced Mail (PEM) applications, as defined in the Internet Standards document:
TIdEncoder3to4 contains a coding table to represent the valid characters in the encoder alphabet.
TIdEncoder3to4 represents 3-byte input values as 4 concatenated 6-bit groups, each of which is translated into a single valid character in the encoder coding table.
Special processing is performed to ensure that data to be encoded is a multiple of 3-bytes. When fewer than 3 bytes are available, a user-definable fill character is used to pad input data to the required length.
TIdEncoder3to4 does not specify the valid characters in the coding table. Application will generally use a descendant class, like TIdCoderMIME or TIdCoderUUE, where the alphabet is specified.
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