.TH LIBKECCAK_ZEROCOPY_UPDATE 3 LIBKECCAK
.SH NAME
libkeccak_zerocopy_update - Partially hash a message without copying
.RB ( ADVANCED )
.SH SYNOPSIS
.nf
#include <libkeccak.h>

void libkeccak_zerocopy_update(struct libkeccak_state *\fIstate\fP, const void *\fImsg\fP, size_t \fImsglen\fP);
.fi
.PP
Link with
.IR -lkeccak .
.SH DESCRIPTION
The
.BR libkeccak_zerocopy_update ()
function continues (or starts) hashing a message.
The current state of the hashing is stored in
.IR *state ,
and will be updated. The message specified by the
.I msg
parameter with the byte-size specified by the
.I msglen
parameter, will be hashed.
.PP
As a restriction specific to the
.BR libkeccak_zerocopy_update ()
function, the
.I msglen
argument must be an integer multiple of the bitrate
divided by eight. This is returned by the
.BR libkeccak_zerocopy_chunksize (3)
function. The
.BR libkeccak_update (3)
or
.BR libkeccak_fast_update (3)
functions can be used to avoid this restriction,
but these, unlike the
.BR libkeccak_zerocopy_update ()
function, will copy the message and move around
copied data.
.SH RETURN VALUES
The
.BR libkeccak_zerocopy_update ()
function does not return a value.
.SH ERRORS
The
.BR libkeccak_zerocopy_update ()
function cannot fail.
.SH NOTES
Neither parameter by be
.I NULL
or 0.
.PP
It is safe call the
.BR libkeccak_zerocopy_update ()
function before the
.BR libkeccak_update (3),
.BR libkeccak_fast_update (3)
.BR libkeccak_digest (3)
and
.BR libkeccak_fast_digest (3)
functions with the same
.I state
argument. However, calling the
.BR libkeccak_zerocopy_update ()
function after the
.BR libkeccak_update (3)
or
.BR libkeccak_fast_update (3)
functions may cause the message
to be misread.
.SH NOTES
For cSHAKE, the
.BR libkeccak_cshake_initialise (3),
must be called, once, immediately after
state initialisation; before the first
call to the
.BR libkeccak_zerocopy_update ()
function.
.SH SEE ALSO
.BR libkeccak_state_initialise (3),
.BR libkeccak_cshake_initialise (3),
.BR libkeccak_zerocopy_chunksize (3),
.BR libkeccak_fast_update (3),
.BR libkeccak_update (3),
.BR libkeccak_fast_digest (3),
.BR libkeccak_zerocopy_digest (3),
.BR libkeccak_digest (3)