google/benchmark

Fail when calculating complexity

Open

#410 opened on Jun 30, 2017

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enhancementgood first issuehelp wanted

Description

When calculating time complexity and the range includes 0 it fails upon evaluation.

void BM_Example(benchmark::State& state)
{
  while (state.KeepRunning())
  {
    int i = state.range(0);
  }
  state.SetComplexityN(state.range(0));
}

BENCHMARK(BM_JumpTable)->RangeMultiplier(2)->Range(0, 1)->Complexity(benchmark::o1);

Result

F:\cruft\benchmark\src\complexity.cc:270: benchmark::ComputeBigO: Check (run.complexity_n) > (0)' Failed. Did you forget to call SetComplexityN?

Contributor guide

Tech stack
cpp
Domain
performance
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Basic C++ knowledgeGoogle Benchmark library familiarity
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75
Research direction
The bug is in the ComputeBigO function in complexity.cc (line 270) where an assertion requires complexity n > 0. When the benchmark range includes 0, state.range(0) returns 0, causing the assertion to fail. Investigate whether the assertion should be relaxed to allow 0, or if the benchmark should handle range(0) differently. Check the existing comments for any proposed fixes.