just_enough

30/06/2020

The C99 <stdint.h> header provides a plethora of type definition for platform-independent safe code: int_fast16_t, for example, provides an integer that plays well with the machine but has at least 16 bits. The int_fastxx_t and int_leastxx_t defines doesn’t guarantee a tight fit, they provide an machine-efficient fit. They find the fastest type of integer for that machine that respects the constraint.

But let’s take the problem the other way around: what about defines that gives you the smallest integer, not for the number of bits (because that’s trivial with intxx_t) but from the maximum value you need to represent?

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Smaller enums

17/10/2017

As you may have noticed, efficient representation of information and data structure is kind of a hobby of mine. I often look at ways I can reduce the memory footprint, and, as often, it’s the small details that are the most annoying, like, for example, enums that use up pretty much anything the compiler feels like.

Indeed, the standard does not require that the compiler uses the smallest type, but merely one that can hold all values (§7.2.6, in ISO/IEC 14882:2011(E)), so you end up with something “convenient”, that is, int. Unless, of course, you do specify storage.

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Fractional Bits (Part III)

18/10/2016

A long time ago, we discussed the problem of using fractions of bits to encode, jointly, values without wasting much bits. But we considered then only special cases, but what if we need to shift precisely by, say, half a bit?

But what does shifting by half a bit even means?

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Storage size from bits

29/03/2016

Last week, we had a look at the computation of Log2 using templates and constexpr. Of course, I had ulterior motives. In particular, I was interested in allocating just the right number of bits for a field in a bit field, but rather than hard-coding it, having it deduced from a template argument. Let’s see how we can do that.

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Log2 (with C++ metaprogramming)

22/03/2016

C++ meta-programming a powerful tool. Not only can you use it to build generic types (such as the STL’s std::list), you can also use it to have compile-time evaluation. Let’s have a look at a simple problem that can be solved in two very different ways: computing the Log base 2 of an integer.

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Of Drunkards

06/08/2013

In a city with orthogonal streets and regular city block, a party-goer leaves a bar and walks back home. His home is North East from the bar, N blocks up, and E blocks east. At each intersection, he decide to go either north or east randomly—but whatever’s left of his sobriety keeps from backtracking: he always moves closer to home. How many ways can the drunkard get get back home?

city

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