Can double be used to store and safely retrieve 128 bit IPv6?

Question

As we know double can store number from ±4.94065645841246544e-324 to ±1.79769313486231570e+308. Can we store 128 bits value like IPv6 in double and retrieve as it is? For example, to store IPv4 we can use a 32 bit integer and store them as 8 bits partition. And we can retrieve them by using bit masking.

There is no standard container to store 128 bit in any language AFAIK. I know double can store 64 bits safely without any precision error but is there any hack?

you cannot store 128 bits of information in less than 128 bits, double usually has 64 bits, so no — BeyelerStudios, Oct 14 '16 at 19:03
Check what the `sizeof(double)` is. If it is not `16` then no. — NathanOliver, Oct 14 '16 at 19:03
No, that won't work. IPv6 addresses are 128-bit integers which have far too many significant digits. Floating point numbers don't have enough significant digits. — Ron Maupin, Oct 14 '16 at 19:03

score 7 · Accepted Answer · edited May 23 '17 at 10:32

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Technically you could, if sizeof(double) * CHAR_BITS ≥ 128 (it's 64bits on my machine), but why would you do that? Instead of reinventing the wheel use sockaddr_in6, or, if you must, an array of uint8_t or a std::bitset.

Related answer: Efficient way to store IPv4/IPv6 addresses

edited May 23 '17 at 10:32

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answered Oct 14 '16 at 19:04

krzaq

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score 3 · Answer 2 · edited May 23 '17 at 12:03

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I would be reluctant to use a double because its size is unspecified.

If you need a 128 bit integer, I would recommend to use non-standard types as explained in this question.

edited May 23 '17 at 12:03

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answered Oct 14 '16 at 19:04

Philipp Claßen

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Can double be used to store and safely retrieve 128 bit IPv6?

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