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(MD5 Checksum): New node, documents the md5 primitive.

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Eli Zaretskii 2001-09-08 17:51:25 +00:00
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lispref/text.texi
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@ -57,6 +57,7 @@ the character after point.
* Registers:: How registers are implemented. Accessing the text or
position stored in a register.
* Base 64:: Conversion to or from base 64 encoding.
* MD5 Checksum:: Compute the MD5 ``message digest''/``checksum''.
* Change Hooks:: Supplying functions to be run when text is changed.
@end menu
@ -3515,7 +3516,13 @@ all markers unrelocated.
Base 64 code is used in email to encode a sequence of 8-bit bytes as
a longer sequence of @sc{ascii} graphic characters. It is defined in
Internet RFC 2045. This section describes the functions for
Internet RFC@footnote{
An RFC, an acronym for @dfn{Request for Comments}, is a numbered
Internet informational document describing a standard. RFCs are
usually written by technical experts acting on their own initiative,
and are traditionally written in a pragmatic, experience-driven
manner.
}2045. This section describes the functions for
converting to and from this code.
@defun base64-encode-region beg end &optional no-line-break
@ -3564,6 +3571,54 @@ decoded text.
The decoding functions ignore newline characters in the encoded text.
@end defun
@node MD5 Checksum
@section MD5 Checksum
@cindex MD5 checksum
@cindex message digest computation
MD5 cryptographic checksums, or @dfn{message digests}, are 128-bit
``fingerprints'' of a document or program. They are used to verify
that you have an exact and unaltered copy of the data. The algorithm
to calculate the MD5 message digest is defined in Internet
RFC@footnote{
For an explanation of what is an RFC, see the footnote in @ref{Base
64}.
}1321. This section describes the Emacs facilities for computing
message digests.
@defun md5 object &optional start end coding-system noerror
This function returns the MD5 message digest of @var{object}, which
should be a buffer or a string.
The two optional arguments @var{start} and @var{end} are character
positions specifying the portion of @var{object} to compute the
message digest for. If they are @code{nil} or omitted, the digest is
computed for the whole of @var{object}.
The function @code{md5} does not compute the message digest directly
from the internal Emacs representation of the text (@pxref{Text
Representations}). Instead, it encodes the text using a coding
system, and computes the message digest from the encoded text. The
optional fourth argument @var{coding-system} specifies which coding
system to use for encoding the text. It should be the same coding
system that you used to read the text, or that you used or will use
when saving or sending the text. @xref{Coding Systems}, for more
information about coding systems.
If @var{coding-system} is @code{nil} or omitted, the default depends
on @var{object}. If @var{object} is a buffer, the default for
@var{coding-system} is whatever coding system would be chosen by
default for writing this text into a file. If @var{object} is a
string, the user's most preferred coding system (@pxref{Recognize
Coding, prefer-coding-system, the description of
@code{prefer-coding-system}, emacs, GNU Emacs Manual}) is used.
Normally, @code{md5} signals an error if the text can't be encoded
using the specified or chosen coding system. However, if
@var{noerror} is non-@code{nil}, it silently uses @code{raw-text}
coding instead.
@end defun
@node Change Hooks
@section Change Hooks
@cindex change hooks