mkieee.c

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#include <stdlib.h>
#include <math.h>
#include "grib2.h"
 
 
void mkieee(g2float *a,g2int *rieee,g2int num)
{
 
    g2int  j,n,ieee,iexp,imant;
    double  atemp;
 
    static double  two23,two126;
    static g2int test=0;
    //g2intu msk1=0x80000000;        // 10000000000000000000000000000000 binary
    //g2int msk2=0x7F800000;         // 01111111100000000000000000000000 binary
    //g2int msk3=0x007FFFFF;         // 00000000011111111111111111111111 binary
 
    if ( test == 0 ) {
        two23=(double)int_power(2.0,23);
        two126=(double)int_power(2.0,126);
        test=1;
    }
 
    for (j=0;j<num;j++) {
 
        ieee=0;
 
        if (a[j] == 0.0) {
            rieee[j]=ieee;
            continue;
        }
 
//
//  Set Sign bit (bit 31 - leftmost bit)
//
        if (a[j] < 0.0) {
            ieee= 1 << 31;
            atemp=-1.0*a[j];
        }
        else {
            ieee= 0 << 31;
            atemp=a[j];
        }
        //printf("sign %ld %x \n",ieee,ieee);
//
//  Determine exponent n with base 2
//
        if ( atemp >= 1.0 ) {
            n = 0;
            while ( int_power(2.0,n+1) <= atemp ) {
                n++;
            }
        }
        else {
            n = -1;
            while ( int_power(2.0,n) > atemp ) {
                n--;
            }
        }
        iexp=n+127;
        if (n >  127) iexp=255;     // overflow
        if (n < -127) iexp=0;
        //printf("exp %ld %ld \n",iexp,n);
        //      set exponent bits ( bits 30-23 )
        ieee = ieee | ( iexp << 23 );
//
//  Determine Mantissa
//
        if (iexp != 255) {
            if (iexp != 0)
                atemp=(atemp/int_power(2.0,n))-1.0;
            else
                atemp=atemp*two126;
            imant=(g2int)rint(atemp*two23);
        }
        else {
            imant=0;
        }
        //printf("mant %ld %x \n",imant,imant);
        //      set mantissa bits ( bits 22-0 )
        ieee = ieee | imant;
//
//  Transfer IEEE bit string to rieee array
//
        rieee[j]=ieee;
 
    }
 
    return;
 
}