Convert from IBM floating point to IEEE floating point standard and Vice Versa- In C#?

问题

Was looking for a way to IEEE floating point numbers to IBM floating point format for a old system we are using.

Is there a general formula we can use in C# to this end.

回答1:

// http://en.wikipedia.org/wiki/IBM_Floating_Point_Architecture
// float2ibm(-118.625F) == 0xC276A000
// 1 100 0010    0111 0110 1010 0000 0000 0000
// IBM/370 single precision, 4 bytes
// xxxx.xxxx xxxx.xxxx xxxx.xxxx xxxx.xxxx
// s|-exp--| |--------fraction-----------|
//    (7)          (24)
// value = (-1)**s * 16**(e - 64) * .f   range = 5E-79 ... 7E+75
static int float2ibm(float from)
{
    byte[] bytes = BitConverter.GetBytes(from);
    int fconv = (bytes[3] << 24) | (bytes[2] << 16) | (bytes[1] << 8)| bytes[0];

    if (fconv == 0) return 0;
    int fmant = (0x007fffff & fconv) | 0x00800000;
    int t = (int)((0x7f800000 & fconv) >> 23) - 126;
    while (0 != (t & 0x3)) { ++t; fmant >>= 1; }
    fconv = (int)(0x80000000 & fconv) | (((t >> 2) + 64) << 24) | fmant;
    return fconv; // big endian order
}

I changed a piece of code called static void float_to_ibm(int from[], int to[], int n, int endian) the code above can be run correctly in PC from is little endian float number. return value is big endian ibm float number but stored in type int.

回答2:

An obvious approach would be to use textual representation of the number as the interchange format.

回答3:

I recently had to convert one float to another. It looks like XDR format uses an odd format for its floats. So when converting from XDR to standard floats, this code did it.

#include <rpc/rpc.h>

// Read in XDR float array, copy to standard float array
// out array needs to be allocated before the function call

bool convertFromXdrFloatArray(float *in, float *out, long size)
{
    XDR xdrs;
    xdrmem_create(&xdrs,(char *)in, size*sizeof(float), XDR_DECODE);

    for(int i = 0; i < size; i++)
    {
        if(!xdr_float(&xdrs, out++)) {
            fprintf(stderr,"%s:%d:ERROR:xdr_float\n",__FILE__,__LINE__);
            exit(1);
        }
    }
    xdr_destroy(&xdrs);

    return true;
}

回答4:

Using first answer I added the following that may be useful in some cases:

///

  /// Converts an IEEE floating number to its string representation (4 or 8 ascii codes).
    /// Useful for SAS XPORT files format.
    /// </summary>
    /// <param name="from_">IEEE number</param>
    /// <param name="padTo8_">When true, output is 8 chars rather than 4</param>
    /// <returns>Printable string according to hardware's endianness</returns>
    public static string Float2IbmAsAsciiCodes(float from_, bool padTo8_ = true)
    {
        StringBuilder sb = new StringBuilder();
        string s;
        byte[] bytes = BitConverter.GetBytes(Float2Ibm(from_)); // big endian order

        if (BitConverter.IsLittleEndian)
        {
            // Revert bytes order
            for (int i = 3; i > -1; i--)
                sb.Append(Convert.ToChar(bytes[i]));
            s = sb.ToString();
            if (padTo8_)
                s = s.PadRight(8, '\0');
            return s;
        }
        else
        {
            for (int i = 0; i < 8; i++)
                sb.Append(Convert.ToChar(bytes[i]));
            s = sb.ToString();
            if (padTo8_)
                s = s.PadRight(8, '\0');
            return s;
        }
    }

来源：https://stackoverflow.com/questions/4550367/convert-from-ibm-floating-point-to-ieee-floating-point-standard-and-vice-versa

标签

floating-point

ieee-754