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package com.j256.simplemagic.endian;

/**
 * Converts values in "little" endian-ness where the high-order bytes come _after_ the low-order (DCBA). x86 processors.
 * 
 * @author graywatson
 */
public class LittleEndianConverter implements EndianConverter {

	LittleEndianConverter() {
		// only EndiaType should construct this
	}

	@Override
	public Long convertNumber(int offset, byte[] bytes, int size) {
		return convertNumber(offset, bytes, size, 8, 0xFF);
	}

	@Override
	public Long convertId3(int offset, byte[] bytes, int size) {
		return convertNumber(offset, bytes, size, 7, 0x7F);
	}

	@Override
	public byte[] convertToByteArray(long value, int size) {
		byte[] result = new byte[size];
		for (int i = 0; i < size; i++) {
			result[i] = (byte) (value & 0xFF);
			value >>= 8;
		}
		return result;
	}

	private Long convertNumber(int offset, byte[] bytes, int size, int shift, int mask) {
		if (offset < 0 || offset + size > bytes.length) {
			return null;
		}
		long value = 0;
		for (int i = offset + (size - 1); i >= offset; i--) {
			value = value << shift | (bytes[i] & mask);
		}
		return value;
	}
}