| Hex Floats

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ISO C99 supports floating-point numbers written not only in the usual decimal notation, such as `1.55e1`, but also numbers such as `0x1.fp3` written in hexadecimal format. As a GNU extension, GCC supports this in C89 mode (except in some cases when strictly conforming). In that format the `0x` hex introducer and the `p` or `P` exponent field are mandatory. The exponent is a decimal number that indicates the power of 2 by which the significant part will be multiplied. Thus `0x1.f` is `1 15/16`, `p3` multiplies it by 8, and the value of `0x1.fp3` is the same as `1.55e1`.
Unlike for floating-point numbers in the decimal notation the exponent is always required in the hexadecimal notation. Otherwise the compiler would not be able to resolve the ambiguity of, e.g., `0x1.f`. This could mean `1.0f` or `1.9375` since `f` is also the extension for floating-point constants of type `float`.