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References: <6c4a456a-3198-bfa2-6d89-433e4d3f3fd5@redhat.com> <06ce80d4-02da-4323-af3b-0d0f8be3f6eb@default>
In-Reply-To: <06ce80d4-02da-4323-af3b-0d0f8be3f6eb@default>
From: "Ard Biesheuvel" <ard.biesheuvel@linaro.org>
Date: Fri, 24 May 2019 17:30:49 +0200
Message-ID: <CAKv+Gu_VqNa-Kg0Wo0rCYf0CUCx0yTGKsCUXHBRyEvtMN+OYWA@mail.gmail.com>
Subject: Re: why does RAND_add() take "randomness" as a "double"?
To: Paul Dale <paul.dale@oracle.com>
Cc: Laszlo Ersek <lersek@redhat.com>, Jian J Wang <jian.j.wang@intel.com>, 
	edk2-devel-groups-io <devel@edk2.groups.io>, "Lu, XiaoyuX" <xiaoyux.lu@intel.com>
Content-Type: text/plain; charset="UTF-8"

(remove openssl user list)

On Wed, 22 May 2019 at 03:48, Paul Dale <paul.dale@oracle.com> wrote:
>
> Double makes sense.  Entropy is often estimated as a real value.
>
> E.g. we have the aforementioned coin flipper feeding data serially.
> Adding each bit sequentially means 0.125 bytes of entropy per call.
>
> Not the best example....
>

It looks like the people saying double is a good idea didn't actually
look at the code. The double argument is compared to a size_t cast to
double, and assigned that same value under some conditions.

I think the problem is that the double argument is part of the RAND
API, so they cannot easily change it.