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agra-uni-bremen / crave

Constrained random stimuli generation for C++ and SystemC
http://systemc-verification.org/crave
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Randomization of SystemC types > 64 bit not supported #4

Open AnthonyVH opened 6 years ago

AnthonyVH commented 6 years ago

Creating an e.g. crave::randv<sc_dt::sc_bv<128>> object works fine. However, when next() is called on this object, only bits 0-63 will be set, the remaining ones will all be zero. This is hardcoded in SystemC.hpp's next function, where an std::int64 generator is used.

I'm not sure how difficult it would be to fix this. Extending the random number generation to generate enough random bits seems doable. Modifying generated constraints to be correct seems like a more difficult task.

Alternatively, construction of such objects could be prevented with some SFINAE, e.g.:

/* Boost is preferred/required over C++14 for compatibility with e.g. QuestaSim. */
template <int N, std::enable_if_t<N <= 64, int> = 0>
struct randv<sc_dt::sc_bv<N>> : public randv_base<sc_dt::sc_bv<N>> { /* etc */ };
hoangmle commented 6 years ago

The main issue here is that ir/Constant uses uint64_t internally. Switching to boost::multiprecision::cpp_int should be enough and can be done with reasonable effort. The downside is that things get a bit slower when you do not use types > 64-bit. I will try this in my next free slot.

AnthonyVH commented 6 years ago

That sounds very promising! This, the RAII, and the vector randomization issues are the only thing holding me back from proposing the use of CRAVE into all our future SysC testbench infrastructure, so I'm loving the quick responses to the issues I opened here :+1:.

hoangmle commented 6 years ago

I have added basic support for this in the branch experimental_bigint, you need to use the experimental API though. There is also a new example https://github.com/hoangmle/crave-examples/blob/experimental_bigint/experimental_api/ex12_bigint/main.cpp Can you try it out to see whether it suits your need and what is still missing? Thanks!

AnthonyVH commented 6 years ago

Awesome! I've been a bit swamped by other things, but as soon as I find this for this again I'll take a look at it (and put together a PR for issue #5).