Work on man pages

Signed-off-by: Mattias Andrée <maandree@kth.se>

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+.TH LIBKECCAK_HMAC_DIGEST 3 LIBKECCAK
+.SH NAME
+libkeccak_hmac_digest - Complete the HMAC-hashing of a message with erasure
+.SH SYNOPSIS
+.LP
+.nf
+#include <libkeccak.h>
+.P
+int
+libkeccak_hmac_digest(libkeccak_hmac_state_t *\fIstate\fP, const char *\fImsg\fP,
+                      size_t \fImsglen\fP, size_t \fIbits\fP, const char *\fIsuffix\fP,
+                      char *\fIhashsum\fP);
+.fi
+.P
+Link with
+.IR -lkeccak .
+.SH DESCRIPTION
+The
+.BR libkeccak_hmac_digest ()
+function absorbes the last part of (or all of) a message,
+and returns the HMAC hash of the entire message. The last
+part of the message is specified by the
+.I msg
+parameter, and its byte-size is specified by the
+.I msglen
+parameter. If all of the message has already be processed
+by calls to the
+.BR libkeccak_hmac_update (3)
+function or the
+.BR libkeccak_hmac_fast_update (3)
+function (with the same pointer on
+.IR state ,)
+.I msg
+and
+.I msglen
+should be set to
+.I NULL
+and 0, respectively.
+.PP
+If the message is not comprised a whole number of bytes,
+the number of bits, modulus 8, in the message should be
+specified in the
+.I bits
+parameter. 
+.I msglen
+must only count the number of whole bytes, that is, the
+floor of the number of bits in the message divided by 8.
+.PP
+.I suffix
+should be a NUL-terminated string of ASCII '1':s
+and '0':s, representing the bits that should be appended
+to the message. If this string is empty,
+.I NULL
+may be used instead. This is used to select hash algorithm.
+For pure Keccak,
+.I NULL
+or "" is used. For the other algorithms the constants
+.B LIBKECCAK_SHA3_SUFFIX
+(for SHA-3),
+.B LIBKECCAK_RAWSHAKE_SUFFIX
+(for RawSHAKE), and
+.B LIBKECCAK_SHAKE_SUFFIX
+(for SHAKE) are used.
+.PP
+The hash of the message will be stored to
+.IR hashsum ,
+unless
+.I hashsum
+is
+.I NULL
+(which increases the performance of the call.) A total of
+.RI (( state->n
++ 7) / 8) bytes will be written to the beginning of
+.IR hashsum .
+Therefore,
+.I hashsum
+needs at least an allocation size of that number of bytes.
+.PP
+The
+.BR libkeccak_hmac_digest ()
+function may reallocate the state's message chunk buffer.
+When doing so, it attempts to do so as securely as possible,
+rather than as fast as possible.
+.SH RETURN VALUES
+The
+.BR libkeccak_hmac_digest ()
+function returns 0 upon successful completion. On error,
+-1 is returned and
+.I errno
+is set to describe the error.
+.SH ERRORS
+The
+.BR libkeccak_hmac_digest ()
+function may fail for any reason specified by the function
+.BR malloc (3).
+.SH SEE ALSO
+.BR libkeccak_hmac_create (3),
+.BR libkeccak_hmac_initialise (3),
+.BR libkeccak_hmac_update (3),
+.BR libkeccak_hmac_fast_digest (3),
+.SH BUGS
+Please report bugs to https://github.com/maandree/libkeccak/issues or to
+maandree@kth.se