把一个IEEE754浮点数转换为IBM370浮点数的C#代码。

 

在这个上有古老的IBM370浮点格式的说明。

 

 

// 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        }

 

在这段C代码的基础上修改的

 

/* Assumes sizeof(int) == 4 */static void float_to_ibm(int from[], int to[], int n, int endian)/********************************************************************** float_to_ibm - convert between 32 bit IBM and IEEE floating numbers*********************************************************************** Input:from       input vectorn          number of floats in vectorsendian     =0 for little endian machine, =1 for big endian machinesOutput:to         output vector, can be same as input vector*********************************************************************** Notes:Up to 3 bits lost on IEEE -> IBMIBM -> IEEE may overflow or underflow, taken care of by substituting large number or zeroOnly integer shifting and masking are used.*********************************************************************** Credits:     CWP: Brian Sumner***********************************************************************/{    register int fconv, fmant, i, t;    for (i=0;i
    
     > 23) - 126;            while (t & 0x3) { ++t; fmant >>= 1; }            fconv = (0x80000000 & fconv) | (((t>>2) + 64) << 24) | fmant;        }        if(endian==0)                fconv = (fconv<<24) | ((fconv>>24)&0xff) |                        ((fconv&0xff00)<<8) | ((fconv&0xff0000)>>8);        to[i] = fconv;    }    return; }
    

 

 

另外找到的一些C代码放在这里以后备用

#include "ibmieee.h"   /*--------------------------------------------------------------------- * *   FILE: ./ibmieee.c * *----------------------------------------------------------------------**   DESCRIPTION:*     Conversion from IBM to IEEE format*     Byte order is detected and accounted for using*     define constant 'L_ENDIAN'**----------------------------------------------------------------------*   ROUTINES DEFINED IN THIS MODULE:                                 *----------------------------------------------------------------------** *  Convert IBM to IEEE integer:**   ibm_ieee_i( n, ibm, ieee)*   int n;*   int *ibm;*   int *ieee;* *  Convert IEEE to IBM integer:**   ieee_ibm_i( n, ieee, ibm)*   int n;*   int *ieee;*   int *ibm;* *  Convert IBM to IEEE short floating point:**   ibm_ieee_f( n, ibm, ieee)*   int n;*   char *ibm;*   float *ieee;* *  Convert IEEE to IBM floating point:**   ieee_ibm_f( n, ieee, ibm)*   int n;*   float *ieee;*   char *ibm;**---------------------------------------------------------------------*/   void ibm_ieee_i( int n, char *ibm, char *ieee ) /*        Convert from IBM to IEEE integer, possibly in-place*/ #ifdef L_ENDIAN {   int j;   char temp;    /* Reverse byte order on little endian machines */   for (j=0; j<4*n; j+=4) {     temp=ibm[j];     ieee[j]=ibm[j+3];     ieee[j+3]=temp;     temp=ibm[j+1];     ieee[j+1]=ibm[j+2];     ieee[j+2]=temp;   }  #else    {     int j;      /* Move words if not same location */      if (ibm != ieee)       for (j=0; j
    
     << 1;     };     /* Discard MSB and decrement exponent 1 more */     tmp1.u = tmp1.u & 0x007FFFFF;     exp--;      /* Check for exponent overflow or underflow */     if (exp & 0xFF00) {       if (exp < 0)         /* Underflow */         ieee[i].c[0] = ieee[i].c[1] = ieee[i].c[2] =            ieee[i].c[3] = '\0';       else {         /* Overflow */ #ifdef L_ENDIAN         ieee[i].c[3] = 0x7F;         ieee[i].c[2] = 0x80;         ieee[i].c[1] = 0x00;         ieee[i].c[0] = 0x00; #else         ieee[i].c[0] = 0x7F;         ieee[i].c[1] = 0x80;         ieee[i].c[2] = 0x00;         ieee[i].c[3] = 0x00; #endif       }       iret = 1;       continue;     }                              /* Move exponent into proper field and set sign bit */     tmp2.u = 0;      #ifdef L_ENDIAN     tmp2.c[3] = (char)exp;     tmp2.u = tmp2.u >> 1;     if (temp.u & 0x00000080)       tmp2.u = tmp2.u | 0x80000000;     else       tmp2.u = tmp2.u & 0x7fffffff; #else     tmp2.c[0] = (char)exp;     tmp2.u = tmp2.u >> 1;     tmp2.u = tmp2.u | (temp.u & 0x80000000); #endif     /* Set output value */     temp.u = tmp1.u | tmp2.u;     ieee[i].c[0] = temp.c[0];     ieee[i].c[1] = temp.c[1];     ieee[i].c[2] = temp.c[2];     ieee[i].c[3] = temp.c[3];       }       return ;     }      /*********************************************************************/  void    ieee_ibm_f( int n, VAL *ieee, VAL *ibm )       {       int i;       VAL temp,tmp1,tmp2;       int exp,rem;        for (i=0; i
     
      > 2) + 64;     /* Normalize mantissa by shifting by (4-remainder) */     if (rem) {       tmp1.u = tmp1.u >> (4-rem);       exp = exp + 1;     }                              /* Move exponent and mantissa bytes into IBM locations */ #ifdef L_ENDIAN     tmp2.u = 0;          tmp2.c[0] = (char)exp;     tmp2.c[1] = tmp1.c[2];     tmp2.c[2] = tmp1.c[1];     tmp2.c[3] = tmp1.c[0];     /* Set sign bit */     if (temp.u & 0x80000000) tmp2.u = tmp2.u | 0x00000080; #else     tmp2.u = tmp1.u;     tmp2.c[0] = (char)exp;     /* Set sign bit */     if (temp.u & 0x80000000) tmp2.u = tmp2.u | 0x80000000; #endif      /* Set output value */     ibm[i].c[0] = tmp2.c[0];     ibm[i].c[1] = tmp2.c[1];     ibm[i].c[2] = tmp2.c[2];     ibm[i].c[3] = tmp2.c[3];       }       return ;     }