如何使用Java解压缩COMP-3数字? [英] How to unpack COMP-3 digits using Java?

问题描述

我的大型机文件很大，该文件中有一些打包的数字.我想知道如何使用Java解压缩以下数字吗?

I have huge mainframe file and there are some packed digits in that file. I would like to know how to unpack following digit using java?

包装数字:?

我阅读了解包数字的教程，发现以下规则计算解包数字所需的字节数:

I read tutorials for unpacking digits and found the following rule to count the number of bytes required to unpack digits :

total_number_of_bytes = (no. of digits + 1) / 2

我编写了以下代码来解压缩数字:

I wrote the following code to unpack digits :

public String unpackData(String packedData, int decimalPointLocation) {
        String unpackedData = "";
        char[] characters = packedData.toCharArray();
        final int impliedPositive = 15;
        final int positiveNumber = 12;
        final int negativeNumber = 13;
        for (int currentCharIndex = 0; currentCharIndex < characters.length; currentCharIndex++) {
            byte[] unpackedDigits = unpackByte((byte) characters[currentCharIndex]);
            if(currentCharIndex == (characters.length - 1)) {
                if(unpackedDigits[1] == impliedPositive || unpackedDigits[1] == positiveNumber) {
                    unpackedData += String.valueOf(unpackedDigits[0]);
                } else if(unpackedDigits[1] == negativeNumber) {
                    unpackedData = "-" + unpackedData;
                }
            } else {
                unpackedData += String.valueOf(unpackedDigits[0]) + String.valueOf(unpackedDigits[1]);
            }
        }
        if(decimalPointLocation > 0) {
            unpackedData = unpackedData.substring(0, (decimalPointLocation - 1)) + 
                            "." + 
                            unpackedData.substring(decimalPointLocation);
        }
        return unpackedData;
    }

    private byte[] unpackByte(byte packedData) {
        byte firstDigit = (byte) (packedData >>> 4);
        firstDigit = setBitsToZero(firstDigit, 4, 8);

        //System.out.println(" firstDigit = "+ firstDigit + ", and its bit string after unpacking = " + getBitString(firstDigit, 7));

        byte secondDigit = setBitsToZero(packedData, 4, 8);
        //System.out.println("second digit = " + secondDigit + ", and its bit string of second digit after unpcking = " + getBitString(secondDigit, 7));

        byte[] unpackedData = new byte[2];
        unpackedData[0] = firstDigit;
        unpackedData[1] = secondDigit;
        return unpackedData;
    }

    private byte setBitsToZero(byte number, int startBitPosition, int endBitPosition) {
        for (int i = startBitPosition; i < endBitPosition; i++) {
            number =  (byte) (number & ~(1 << i));
        }
        return number;
    }

此程序对于整数类型值正确运行，但不适用于浮点类型值.

This program works correctly for integer type values but it's not working for floating point type values.

有人可以告诉我我的程序是否正确吗?

Can anyone please tell if my program is correct?

推荐答案

COMP-3(或压缩十进制")数据如下:0x12345s，其中"s"是C表示正，D表示负，或F表示未签名.因此，0x12345c->"12345"，x012345d->"-12345"和0x12345f->"12345".

COMP-3 (or "packed decimal") data looks like this: 0x12345s, where "s" is C for positive, D for negative, or F for unsigned. Thus 0x12345c -> "12345", x012345d -> "-12345", and 0x12345f -> "12345".

您有一个明显的错误:如果符号为负，则忽略包含符号nybble(例如，上面的"5")的字节中的nybble.此外，您在处理半字节时工作非常努力，这是一个简单的按位或4位移位来隔离半字节的操作.

You've got one obvious error: You're ignoring the nybble in the byte that contains the sign nybble (e.g., "5" above) if the sign is negative. In addition, you're working too hard at manipulating the nybbles, it's a simple bitwise-and or a 4-bit shift to isolate a nybble.

尝试类似的操作(未经测试):

Try something like this (untested):

public String unpackData(String packedData, int decimalPointLocation) {
    String unpackedData = "";
    char[] characters = packedData.toCharArray();
    final int negativeSign = 13;
    for (int currentCharIndex = 0; currentCharIndex < characters.length; currentCharIndex++) {
        byte firstDigit = ((byte) characters[currentCharIndex]) >>> 4);
        byte secondDigit = ((byte) characters[currentCharIndex]) & 0x0F;
        unpackedData += String.valueOf(firstDigit);
        if (currentCharIndex == (characters.length - 1)) {
            if (secondDigit == negativeSign) {
                unpackedData = "-" + unpackedData;
            }
        } else {
            unpackedData += String.valueOf(secondDigit);
        }
    }
    if (decimalPointLocation > 0) {
        unpackedData = unpackedData.substring(0, (decimalPointLocation - 1)) + 
                        "." + 
                        unpackedData.substring(decimalPointLocation);
    }
    return unpackedData;
}

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