For example:

float hex_floats(void)
{
    return 0x1.fp3; // 1 15/16 * 2^3
}

In hexadecimal format the exponent is a decimal number that indicates the power of two by which the significant part is multiplied. Therefore 0x1.fp3= 1.9375*8=1.55e1.

C99 also adds %a and %A format for printf().