#include <math.h>
#include <stdio.h>

int show(double x,int (*print)(void* ctx,const char* s),void* ctx) {
    enum { k_max=52 }; char buf[2];
    int k,e,z; double frac;
    if (x==0) {
        if (1/x<0) print(ctx,"-");
        return print(ctx,"0");
    }
    if (x<0) print(ctx,"-");
    if (x!=x) return print(ctx,"NAN");
    if (2*x==x) return print(ctx,"INF");
    if (x<0) x=-x;
    e=floor(log2(x));
    frac=x*pow(2,-e);
    //{ long long f=floor((frac-1)*pow(2.0,k_max)); printf(" f=%013llX ",f); }
    print(ctx,"1.");
    for(k=0;k<k_max;++k) {
        if (frac>=1) frac-=1;
        frac*=2;
        if (frac>=1) print(ctx,"1"); else print(ctx,"0");
    }
    print(ctx,"p");
    if (e<0) { print(ctx,"-"); e=-e; }
    z=10; while (z<=e) z*=10;
    for(buf[1]=0;z>=10;) { 
        z/=10; buf[0]='0'+(e/z%10);
        print(ctx,buf);
    }
    return 0;
}

int print(void*,const char* s) { printf("%s",s); return 0; }
void check(double x,const char* s) {
    printf("%s = ",s);
    show(x,print,0); 
    printf("\n");
}

int main(int argc, char const *argv[]) {
    check(1          , "1    ");
    check(2          , "2    ");
    check(100        , "100  ");
    check(0.5        , "0.5  ");
    check(0.125      , "0.125");
    check(1.5        , "1.5  ");
    check(1.0/3      , "1/3  ");
    check(-1.0/3     , "-1/3 ");
    check(1e-30      , "1e-30");
    check(1e+30      , "1e+30");
    check( 0.0       , "0    ");
    check(-0.0       , "-0   ");
    check(1/sqrt(0)  , "+INF ");
    check(-1/sqrt(0) , "-INF ");
    check(sqrt(-1)   , "NAN  ");
    return 0;
}

1     = 1.0000000000000000000000000000000000000000000000000000p0
2     = 1.0000000000000000000000000000000000000000000000000000p1
100   = 1.1001000000000000000000000000000000000000000000000000p6
0.5   = 1.0000000000000000000000000000000000000000000000000000p-1
0.125 = 1.0000000000000000000000000000000000000000000000000000p-3
1.5   = 1.1000000000000000000000000000000000000000000000000000p0
1/3   = 1.0101010101010101010101010101010101010101010101010101p-2
-1/3  = -1.0101010101010101010101010101010101010101010101010101p-2
1e-30 = 1.0100010010000100101111111110111010111100001010100000p-100
1e+30 = 1.1001001111100101100100111001101000001000110011101010p99
0     = 0
-0    = -0
+INF  = INF
-INF  = -INF
NAN   = NAN