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Java parser for the Standard for the Exchange of Earthquake Data (SEED)

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package edu.iris.dmc.seedcodec;

public class Cdsn {

	/* mask for mantissa */
	public static final int MANTISSA_MASK = 0x3fff;

	/* mask for gainrange factor */
	public static final int GAINRANGE_MASK = 0x0003;

	/* # bits in mantissa */
	public static final int SHIFT = 14;

	/* maximum 14 bit positive # */
	public static final int MAX14 = 0x1fff;

	public static int[] decode(byte[] b, int numSamples, boolean swapBytes)
			throws CodecException {
		if (b.length < numSamples * 2) {
			throw new CodecException("Not enough bytes for " + numSamples
					+ " samples, need " + (2 * numSamples) + " but only have "
					+ b.length);
		}
		int[] out = new int[numSamples];
		for (int j = 0; j < out.length; j++) {

			int mult = 0;
			int temp = Utility.bytesToShort(b[2 * j], b[2 * j + 1], swapBytes);
			int mantissa = temp & MANTISSA_MASK;
			int gainrange = (temp >> SHIFT ) & GAINRANGE_MASK;

			/* determine multiplier from gain range factor and format definition */
			/* because shift operator is used later, these are powers of two */
			if (gainrange == 0) {
				mult = 0;
			} else if (gainrange == 1) {
				mult = 2;
			} else if (gainrange == 2) {
				mult = 4;
			} else if (gainrange == 3) {
				mult = 7;
			}

			/* unbias the mantissa */
			mantissa -= MAX14;

			/* calculate sample from mantissa and multiplier using left shift */
			/* mantissa << mult is equivalent to mantissa * (2 exp (mult)) */
			out[j] = (mantissa << mult);

		}
		return out;
	}

}