random: Randomizer::getFloat(): Fix check for empty open intervals #10185
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The check for invalid parameters for the IntervalBoundary::OpenOpen variant was not correct: If two consecutive doubles are passed as parameters, the resulting interval is empty, resulting in an uint64 underflow in the γ-section implementation. Instead of checking whether `$min < $max`, we must check that there is at least one more double between `$min` and `$max`, i.e. it must hold that: nextafter($min, $max) != $max Instead of duplicating the comparatively complicated and expensive `nextafter` logic for a rare error case we instead return `NAN` from the γ-section implementation when the parameters result in an empty interval and thus underflow. This allows us to reliably detect this specific error case *after* the fact, but without modifying the engine state. It also provides reliable error reporting for other internal functions that might use the γ-section implementation.
TimWolla
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This extends the empty-interval check in the γ-section implementation with a check that min is actually the smaller of the two parameters.
cmb69
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Dec 30, 2022
Co-authored-by: Christoph M. Becker <cmbecker69@gmx.de>
Girgias
approved these changes
Dec 30, 2022
zeriyoshi
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Jan 10, 2023
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The check for invalid parameters for the IntervalBoundary::OpenOpen variant was not correct: If two consecutive doubles are passed as parameters, the resulting interval is empty, resulting in an uint64 underflow in the γ-section implementation.
Instead of checking whether
$min < $max, we must check that there is at least one more double between$minand$max, i.e. it must hold that:Instead of duplicating the comparatively complicated and expensive
nextafterlogic for a rare error case we instead returnNANfrom the γ-section implementation when the parameters result in an empty interval and thus underflow.This allows us to reliably detect this specific error case after the fact, but without modifying the engine state. It also provides reliable error reporting for other internal functions that might use the γ-section implementation.