Okay, so I've figured out how to convert both fields. B4 fields are very straightforward. They are essentially a 4-byte array which can be converted to an integer.
//The IBM 5110 were big endian machines, so reverse the array
if (BitConverter.IsLittleEndian)
Array.Reverse(by);
int value = BitConverter.ToInt32(by, 0);
The L8 fields are 8-bytes arrays that represented an IBM Double Precision Float. There are many ways this can be converted to an IEEE 754 Float. A few examples can be found at:
- How To Read IBM 370 Data from a Binary File
- Transform between IEEE, IBM or VAX floating point number formats and bytes expressions
Here's the version I used based on guidance from the articles.
private double IbmFloatToDouble(byte[] value)
{
if (ReferenceEquals(null, value))
throw new ArgumentNullException("value");
if (BitConverter.ToInt64(value, 0) == 0)
return 0;
int exponentBias = 64;
int ibmBase = 16;
double sign = 0.0D;
int signValue = (value[0] & 0x80) >> 7;
int exponentValue = (value[0] & 0x7f);
double fraction1 = (value[1] << 16) + (value[2] << 8) + value[3];
double fraction2 = (value[4] << 24) + (value[5] << 16) + (value[6] << 8) + value[7];
double exponent24 = 16777216.0; // 2^24
double exponent56 = 72057594037927936.0; // 2^56
double mantissa1 = fraction1 / exponent24;
double mantissa2 = fraction2 / exponent56;
double mantissa = mantissa1 + mantissa2;
double exponent = Math.Pow(ibmBase, exponentValue - exponentBias);
if (signValue == 0)
sign = 1.0;
else
sign = -1.0;
return (sign * mantissa * exponent);
}