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Fix UB in benchmark #96

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Fix UB in benchmark #96

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@hebasto hebasto commented Jun 2, 2025 •
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From https://en.cppreference.com/w/c/language/operator_arithmetic.html:

The behavior is undefined if rhs is negative or is greater or equal the number of bits in the promoted lhs.

Steps to reproduce on Ubuntu 25.04 using the master branch @ ea8f66b:

$ ./autogen.sh
$ ./configure --enable-benchmark CXX=clang++-20 CXXFLAGS="-O0"
$ make bench -j $(nproc) bench
$ ./bench
<snip>
recover[ms]	 63	 260.72278	         -	  62.21269	
create[ns]	 63	  79.66483	         -	  17.74962	
/usr/lib/gcc/x86_64-linux-gnu/15/../../../../include/c++/15/bits/uniform_int_dist.h:108: std::uniform_int_distribution<unsigned long>::param_type::param_type(_IntType, _IntType) [_IntType = unsigned long]: Assertion '_M_a <= _M_b' failed.
Aborted (core dumped)

@hebasto hebasto mentioned this pull request Jun 2, 2025
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@hebasto hebasto force-pushed the 250602-bench-ub branch from abc7bef to b0919e1 Compare July 2, 2025 08:54
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hebasto commented Jul 2, 2025

Rebased.

Added a commit that re-enables the now-fixed benchmarks in CI.

sipa
sipa reviewed Oct 21, 2025
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src/bench.cpp Outdated
std::vector<uint64_t> roots(2 * syndromes);
std::random_device rng;
std::uniform_int_distribution<uint64_t> dist(1, (uint64_t(1) << bits) - 1);
uint64_t upper_bound;
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There is a simpler way:

auto upper_bound = std::numeric_limits<uint64_t>::max() >> (64 - bits);

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Thanks! Taken.

hebasto and others added 2 commits October 21, 2025 10:40
@hebasto @sipa
Fix UB in benchmark
2ab2249 
From https://en.cppreference.com/w/c/language/operator_arithmetic.html:
> The behavior is undefined if rhs is negative or is greater or equal
> the number of bits in the promoted lhs.

Co-authored-by: Pieter Wuille <[email protected]>
@hebasto
ci: Enable benchmarks for all Windows jobs
a436966
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@hebasto @sipa