如何用Java解码ascii文件中的comp3压缩字段？

Question

我有一个从遗留系统中提取的大型机文件。该文件以ascii格式编码。我想把它转换成Comp3。java中有什么算法可以做到这一点吗？另外，我需要帮助如何解压缩comp3字段。我试着用java代码解压缩comp3，但是我发现了不正确的结果

请参考解压缩comp3字段的代码

import java.math.BigInteger;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

/**
 * Converts between integer and an array of bytes in IBM mainframe packed
 * decimal format. The number of bytes required to store an integer is (digits +
 * 1) / 2. For example, a 7 digit number can be stored in 4 bytes. Each pair of
 * digits is packed into the two nibbles of one byte. The last nibble contains
 * the sign, 0F for positive and 0C for negative. For example 7654321 becomes
 * 0x76 0x54 0x32 0x1F.
 **/ 


public class PackedDecimalToComp {

    public static void main(String[] args) {

        try {
            // test.unpackData(" 0x12345s");
            Path path = Paths.get("C:\\Users\\AV00499269\\Desktop\\Comp3 data file\\Comp3Test.txt");
            byte[] data = Files.readAllBytes(path);
            PackedDecimalToComp test = new PackedDecimalToComp();
            test.unpackData(data);
        } catch (Exception ex) {
            System.out.println("Exception is :" + ex.getMessage());
        }    
    }

    private static String unpackData(byte[] packedData) {
        String unpackedData = "";

        final int negativeSign = 13;
        for (int currentCharIndex = 0; currentCharIndex < packedData.length; currentCharIndex++) {
            byte firstDigit = (byte) ((packedData[currentCharIndex] >>> 4) & 0x0F);
            byte secondDigit = (byte) (packedData[currentCharIndex] & 0x0F);
            unpackedData += String.valueOf(firstDigit);
            if (currentCharIndex == (packedData.length - 1)) {
                if (secondDigit == negativeSign) {
                    unpackedData = "-" + unpackedData;
                }
            } else {
                unpackedData += String.valueOf(secondDigit);
            }
        }
        System.out.println("Unpackeddata is :" + unpackedData);

        return unpackedData;
    }    
}

Answer 1

代码中的注释不正确。带正号的打包数据在最后一次啃中有x'a'、x'c'、x'e'或x'f'。大型机也有一个“首选符号”的概念，即在最后一次啃中的x'C'表示正，在最后一次啃中的x'D'表示负。

大型机数据通常在单个记录中同时包含文本和二进制数据，例如名称、货币金额和数量：

漏斗恩典%。

...应该是...

X'C8969797859940404040C79981838540404040404081996C004B'