[fhgffy]

Detail::bootstrap() could index past the end of the resample, as reported in #3214.

If all jackknife estimates are equal, sum_squares is 0 and the acceleration is 0 / 0 = NaN. That makes a1/a2 NaN, std::lround(NaN) returns LONG_MIN, and since hi was only clamped from above it becomes a huge size_t. On Linux with a 64-bit long the index times sizeof(double) wraps around to resample[0], so the upper bound silently comes out below the point estimate; with a 32-bit long (MinGW, as in the issue) it is a real out-of-bounds read and crashes. The same thing happens when every resampled estimate is below the point estimate and the acceleration is non-zero, because bias is then infinite and a(b) turns into inf/inf.

Changes:

• zero jackknife variance now means zero acceleration instead of NaN
• both indices are clamped to [0, n - 1]; if the adjusted quantile is still NaN, lo falls back to 0 and hi to n - 1

Added a test case to InternalBenchmark.tests.cpp that calls bootstrap() with both inputs. Before the change it fails with upper_bound 22.0 == 24 and 0.5 == 2 (the wrapped-around resample[0]); with it, it passes. Approval baselines are updated for the new test case, and the full ctest run passes on Linux (GCC 14).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.42%. Comparing base (0809213) to head (bb06231).

Additional details and impacted files

@@            Coverage Diff             @@
##            devel    #3216      +/-   ##
==========================================
+ Coverage   91.18%   91.42%   +0.24%     
==========================================
  Files         205      205              
  Lines        9101     9104       +3     
==========================================
+ Hits         8298     8323      +25     
+ Misses        803      781      -22     

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[horenmar]

Thanks