expchk.c

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//
// EXPCHK    : analyze floating point exponents
//

#include "ftnstd.h"

// If x is a real or double precision number, let xm be the magnitude of x.
// If xm is such that 10**d1 <= xm < 10**d2 the output is produced using
// 0PFw.d; otherwise 1PEw.dEe is used.
// We have chosen d1=3, d2=7, w=24, d=15 (double precision) or d=7 (real).


bool    ToFFormat( reallong val ) {
//=================================

// Check if floating point value can be displayed using F format.

    int         exp;

    exp = ((unsigned_16 *)(&val))[3] & 0x7ff0;
    if( exp == 0 ) return( TRUE );
    exp >>= 4;
    exp -= 0x03ff;      // unbias exponent
    // 2**19 < 10**7 < 2**20
    if( exp >= 20 ) return( FALSE );
    if( exp == 19 ) {
        // 1000000 is  0x412e848000000000
        if( ( ((unsigned_32 *)(&val))[1] & 0x7fffffff ) >= 0x412e8480 ) {
            return( FALSE );
        }
    }
    exp = -exp;
    if( exp >= 12 ) return( FALSE );
    return( TRUE );
}