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+.TH LIBKECCAK_FAST_UPDATE 3 LIBKECCAK
+.SH NAME
+libkeccak_fast_update - Partially hash a message without erasure
+.SH SYNOPSIS
+.LP
+.nf
+#include <libkeccak.h>
+.P
+int
+libkeccak_fast_update(libkeccak_state_t *\fIstate\fP, const char *\fImsg\fP,
+                      size_t \fImsglen\fP);
+.fi
+.P
+Link with
+.IR -lkeccak .
+.SH DESCRIPTION
+The
+.BR libkeccak_fast_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
+The
+.BR libkeccak_fast_update ()
+function may reallocate the state's message chunk buffer.
+When doing so, it attempts to do so as quickly as possible,
+rather than ensuring that the information in the old
+allocation is securely removed if a new allocation is required.
+.SH RETURN VALUES
+The
+.BR libkeccak_fast_update ()
+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_fast_update ()
+function may fail for any reason specified by the function
+.BR realloc (3).
+.SH NOTES
+Neither parameter by be
+.I NULL
+or 0.
+.SH EXAMPLE
+This example calculates the Keccak[b = 1024, c = 576, n = 256]
+hash of the input from stdin, and prints the hash, in hexadecimal
+form, to stdout.
+.LP
+.nf
+libkeccak_state_t state;
+libkeccak_spec_t spec;
+char binhash[256 / 8];
+char hexhash[256 / 8 * 2 + 1];
+char chunk[4 << 10];
+ssize_t len;
+
+spec.bitrate = 1024;
+spec.capacity = 576;
+spec.output = 256;
+if (libkeccak_state_initialise(&state, &spec) < 0)
+    goto fail;
+
+for (;;) {
+    len = read(STDIN_FILENO, chunk, sizeof(chunk));
+
+    if ((len < 0) && (errno == EINTR))
+        continue;
+    if (len < 0)
+        goto fail;
+    if (len == 0)
+        break;
+
+    if (libkeccak_fast_update(&state, chunk, (size_t)len) < 0)
+        goto fail;
+}
+if (libkeccak_fast_digest(&state, NULL, 0, 0, "", binhash) < 0)
+    goto fail;
+
+libkeccak_behex_lower(hexhash, binhash, sizeof(binhash));
+printf("%s\\n", hexhash);
+libkeccak_state_fast_destroy(&state);
+.fi
+.SH SEE ALSO
+.BR libkeccak_state_initialise (3),
+.BR libkeccak_update (3),
+.BR libkeccak_fast_digest (3),
+.BR libkeccak_digest (3)
+.SH BUGS
+Please report bugs to https://github.com/maandree/libkeccak/issues or to
+maandree@kth.se