[hdrhistogram]: Prevent an FPE in rd_hdr_histogram_new (#4949) #5197
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…4949) The Floating Point Exception (FPE) `FE_DIVBYZERO` is flagged in `rd_hdr_histogram_new` when `log2()` is called with `0`. This is done in `rd_avg_init` numerous times, some of which cannot be disabled in recent versions. Consumers of librdkakfa may enable the raising of exceptions when FPEs occur, including `FE_DIVBYZERO`, which causes the function to fail. It is reasonable for the callers of `rd_hdr_histogram_new` to pass `0` for the `minValue` parameter, and the intention of the calculation of `unitMagnitude` is also reasonable. As such, fixing the maths there is the correct approach. `unitMagnitude` being `0` in this case is an apt choice based on how log2(n) works for n near `0`, and that the caluclation already minimises to `0`. A simple test was included that resets the flags, runs the offending function, and observes the new set flags. Appropriately, it fails before the fix, and passes after.
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Was unable to get trivup to work correctly, will try again as soon as I can (most likely next week; business trip). |
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First time doing a Pull Request on an open source project so please bear with me. :) Fixes #4949
I believe I have followed the contributing guidelines correctly; I have:
make style-check-changedon the source file I changed and the source file I added.CHANGELOG.md.make release-test. (TODO - I need to install trivup for that).Potential issue in build config
One potential issue is that I had to modify the build process to link
test-runnerwith-lrdkafka-staticbecause it did not find the definition forrd_hdr_histogram_new. I assume this is something wrong with my build configuration, but if not we will need to do something to rectify it.