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MSFTBX - Mass Spectrometry File Tool Box

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/*
	IntDecoder.java
	[email protected]

	Copyright 2013 Johan Teleman

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
 */
package umich.ms.external.msnumpress;

/**
 * Decodes ints from the half bytes in bytes. Lossless reverse of encodeInt,
 * although not symmetrical in input arguments.
 */
class IntDecoder {

    int pos = 0;
    boolean half = false;
    byte[] bytes;

    public IntDecoder(byte[] _bytes, int _pos) {
        bytes = _bytes;
        pos = _pos;
    }

    public long next() {
        int head;
        int i, n;
        long res = 0;
        long mask, m;
        int hb;

        if (!half)
            head = (0xff & bytes[pos]) >> 4;
        else
            head = 0xf & bytes[pos++];

        half = !half;

        if (head <= 8)
            n = head;
        else {
            // leading ones, fill in res
            n = head - 8;
            mask = 0xf0000000;
            for (i = 0; i < n; i++) {
                m = mask >> (4 * i);
                res = res | m;
            }
        }

        if (n == 8) return 0;

        for (i = n; i < 8; i++) {
            if (!half)
                hb = (0xff & bytes[pos]) >> 4;
            else
                hb = 0xf & bytes[pos++];

            res = res | (hb << ((i - n) * 4));
            half = !half;
        }

        return res;
    }
}