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Date: Wed, 15 Jan 2014 17:38:57 +0000
From: Peter Maxwell <>
Cc: Solar Designer <>
Subject: Re: [PHC] A must read...

On 15 January 2014 17:26, Krisztián Pintér <> wrote:

> Solar Designer (at Wednesday, January 15, 2014, 3:54:15 PM):
> > Besides integer multiply, I was considering floating-point
> since it came up, i use this opportunity to ask the list:
> how reliable floating point is from interop standpoint? i mean:
> 1, the in-memory storage of single and double types. can we expect
> different architectures having same bit pattern for the same value?
> 2, exact results. should we expect different architectures supporting
> the same type (like IEEE 754) to produce different results due to
> different rounding or otherwise?
> so at the end, my question for example is: if we take two 32 bit
> words, treat them as singles, convert them to doubles, multiply them,
> and then store the resulting double in a 64 bit word, can we expect
> different architectures end up with different bit patterns?

​Well, using floats in cryptography is not exactly a new idea but I suspect
it does have some portability problems, e.g. there's implementation of
Bernstein's poly1305​ using floating point - -
although I haven't actually sat down to look at it... it's sitting fairly
far down on my to-do list.

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