One of the integer part or the fractional part may be elided; one of the decimal point
or the exponent part may be elided.
An exponent value exp scales the mantissa (integer and fractional part) by 10<sup>exp</sup>.
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A hexadecimal floating-point literal consists of a <code>0x</code> or <code>0X</code>
prefix, an integer part (hexadecimal digits), a radix point, a fractional part (hexadecimal digits),