Messages in this thread | | | From | James Bottomley <> | Subject | Re: [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for string_get_size() interface | Date | Tue, 3 Nov 2015 21:19:26 +0000 |
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On Tue, 2015-11-03 at 21:57 +0100, Rasmus Villemoes wrote: > On Tue, Nov 03 2015, James Bottomley <jbottomley@odin.com> wrote: > > > > > It was a suggestion when I explained what the missing sources of > > precision were, I don't think it's really a suggestion when it comes > > with an exemplary patch. > > ex·em·pla·ry > adjective > > 1. > serving as a desirable model; representing the best of its kind. > > Said exemplary patch produces "1.10 KiB" for size=2047, > blk_size=1. (This is caused by the introduction of rounding, and is > probably fixable.) > > James, I do understand the algorithm you're trying to use. What I don't > understand is why you insist on using the approach of reducing size and > blk_size all the way before multiplying them. It seems much simpler to > just reduce them till they're below U32_MAX (not keeping track of any > remainders at that point), multiply them, and then proceed as usual, > This avoids having to deal with weird cross-multiplication terms, gives > more accurate results (yes, I tested that) and avoids the extra 64/32 > division you introduce by decrementing i.
Well, wood and trees, I think. I don't believe there's any more accuracy with the second order term, but it is a lot simpler for anyone to understand. I'll post a v2.
James
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