IBM to IEEE floating point conv

Question

Is there any standard method in java to convert IBM 370(in the form of bytes) to IEEE format.?Any algorithm for the conversion would help..

I tried writing a java code..But i fail to understand where do i go wrong. When i give the input as -2.000000000000000E+02, i'm getting the value as -140.0 in IEEE format. and in othercase when i give the input as 3.140000000000000E+00 i'm getting the value as 3.1712502374909226 in IEEE format Any help on this would be highly appreciated

private void conversion() {
    byte[] buffer = //bytes to be read(8 bytes);
    int sign = (buffer[0] & 0x80);
    // Extract exponent.
    int exp = ((buffer[0] & 0x7f) - 64) * 4 - 1;
    //Normalize the mantissa.
    for (int i = 0; i < 4; i++) {//since 4 bits per hex digit
        if ((buffer[1] & 0x80) == 0) {
            buffer = leftShift(buffer);
            exp = exp - 1;
        }
    }

    // Put sign and mantissa back in 8-byte number
    buffer = rightShift(buffer);// make room for longer exponent
    buffer = rightShift(buffer);
    buffer = rightShift(buffer);
    exp = exp + 1023;//Excess 1023 format
    int temp = exp & 0x0f;//Low 4 bits go into B(1)
    buffer[1]= (byte)((buffer[1]&0xf) | (temp *16));
    buffer[0]= (byte)(sign | ((exp/16) & 0x7f));
    }

     private byte[] rightShift(byte[] buf) {
    int newCarry = 0;
    int oldCarry = 0;
    for(int i = 1; i<buf.length; i++) {
        newCarry = buf[i] & 1;
        buf[i] = (byte)((buf[i] & 0xFE)/2 + (oldCarry != 0 ? 0x80 : 0));
        oldCarry = newCarry;
    }
    return buf;
}

private byte[] leftShift(byte[] buf) {
    int newCarry = 0;
    int oldCarry = 0;
    for(int i = buf.length-1; i>0; i--) {
        newCarry = buf[i] & 1;
        buf[i] = (byte)((buf[i] & 0x7F)*2 + (oldCarry != 0 ? 1 : 0));
        oldCarry = newCarry;
    }   
    return buf;
}

Answer 1

I can see a couple different solutions to your question:

• Use the text representation as an intermediary reference
• Do a straight conversion C code

Answer 2

This IBM Technical Article includes algorithms for converting from IBM floating point formats to IEE floating point.