revamp the original pure Erlang implementation

.gitignore

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+*~
+.eunit
+c_src/config.h
+c_src/*.o
+doc
+ebin
+priv

AUTHORS

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+Steve Vinoski <vinoski@ieee.org>

LICENSE

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+Copyright (c) 2009-2011 Stephen B. Vinoski
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+
+1. Redistributions of source code must retain the above copyright
+   notice, this list of conditions and the following disclaimer.
+2. Redistributions in binary form must reproduce the above copyright
+   notice, this list of conditions and the following disclaimer in the
+   documentation and/or other materials provided with the distribution.
+3. Neither the name of the copyright holder nor the names of contributors
+   may be used to endorse or promote products derived from this software
+   without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTOR(S) ``AS IS'' AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTOR(S) BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGE.

README.md

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+# SHA-224, SHA-256, SHA-384, SHA-512 implemented in Erlang NIFs.
+
+## Description
+
+The **erlsha2** library application implements the SHA-2 Secure Hash Standard
+(SHA-224, SHA-256, SHA-384, SHA-512) using Erlang NIFs. It also
+provides pure Erlang implementations, though they are much slower than
+the C NIF implementations.
+
+See the following links for details:
+
+* (Secure Hash Standard)[href="http://csrc.nist.gov/publications/fips/fips180-3/fips180-3_final.pdf"]
+* (Wikipedia SHA1 article)[href="http://en.wikipedia.org/wiki/SHA1"]
+
+The code implemented here was written by simply following the
+algorithm descriptions provided in the standard. Provided functions
+follow the same style as those found in the standard Erlang `crypto`
+module: for each hash variant there's a simple function returning a
+binary digest and a set of three functions for initializing a digest
+context, updating the context with additional data to be hashed, and
+finalizing the context to get a binary digest result.
+
+## Building and Installing
+
+The **erlsha2** app is built with
+[rebar](https://github.com/basho/rebar), which must be in the command `PATH`.
+
+### Erlang Version
+
+The **erlsha2** app requires Erlang R14B or later.

c_src/config.sh

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+#!/usr/bin/env bash
+
+set -e
+
+CONFIG_HDR=c_src/config.h
+
+if [[ $1 = clean ]]; then
+    rm -f $CONFIG_HDR
+    exit 0
+fi
+
+[[ -n "$CC" ]]
+
+tmpfile=`mktemp /tmp/erlsha2.XXXXXX`
+tmpcfile=${tmpfile}.c
+trap "rm -f $tmpfile $tmpcfile" EXIT
+mv $tmpfile $tmpcfile
+echo '#include <stdint.h>' > $tmpcfile
+if $CC $CFLAGS -c -o /dev/null $tmpcfile 2>/dev/null ; then
+    echo '#define HAVE_STDINT_H 1' > $CONFIG_HDR
+else
+    echo '#include <inttypes.h>' > $tmpcfile
+    if $CC $CFLAGS -c -o /dev/null $tmpcfile 2>/dev/null ; then
+        echo '#define HAVE_INTTYPES_H 1' > $CONFIG_HDR
+    else
+        echo 'neither <stdint.h> nor <inttypes.h> found, aborting' 1>&2
+        exit 1
+    fi
+fi
+
+v='16#12345678'
+prog="case <<$v:32/native>> of <<$v:32/big>> -> 0; <<$v:32/little>> -> 1 end"
+if erl -noinput -noshell -eval "halt($prog)."; then
+    echo '#define WORDS_BIGENDIAN 1' >> $CONFIG_HDR
+else
+    echo '#undef WORDS_BIGENDIAN' >> $CONFIG_HDR
+fi
+
+exit 0