[UBSAN] HGCalVFECompressionImpl: shift exponent 4294967295

[smuzaffar]

We have few UBSAN runtime errors [a]. This happens when exponent (const uint32_t exponent = bitlen - mantissaBits_;) is 1 which causes exponent-2 to become 4294967295 at https://github.com/cms-sw/cmssw/blob/master/L1Trigger/L1THGCal/src/HGCalVFECompressionImpl.cc#L53

@cms-sw/l1-l2 , can you please look in this code and provide a fix ?

[a] https://cmssdt.cern.ch/SDT/jenkins-artifacts/ubsan_logs/CMSSW_14_2_X_2024-10-20-2300/logs/19/19a823aeb7adc34647332f165d28b627/log

23634.0/step2:L1Trigger/L1THGCal/src/HGCalVFECompressionImpl.cc:53:42: runtime error: shift exponent 4294967295 is too large for 64-bit type 'long unsigned int'
24034.0/step2:L1Trigger/L1THGCal/src/HGCalVFECompressionImpl.cc:53:42: runtime error: shift exponent 4294967295 is too large for 64-bit type 'long unsigned int'
24834.0/step2:L1Trigger/L1THGCal/src/HGCalVFECompressionImpl.cc:53:42: runtime error: shift exponent 4294967295 is too large for 64-bit type 'long unsigned int'
24834.911/step2:L1Trigger/L1THGCal/src/HGCalVFECompressionImpl.cc:53:42: runtime error: shift exponent 4294967295 is too large for 64-bit type 'long unsigned int'

[smuzaffar]

assign l1

[cmsbuild]

New categories assigned: l1

@aloeliger,@epalencia you have been requested to review this Pull request/Issue and eventually sign? Thanks

[cmsbuild]

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[cmsbuild]

A new Issue was created by @smuzaffar.

@Dr15Jones, @antoniovilela, @makortel, @mandrenguyen, @rappoccio, @sextonkennedy, @smuzaffar can you please review it and eventually sign/assign? Thanks.

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[makortel]

assign upgrade

[cmsbuild]

New categories assigned: upgrade

@Moanwar,@srimanob,@subirsarkar you have been requested to review this Pull request/Issue and eventually sign? Thanks

[aloeliger]

@jbsauvan You're the name on HGCal I know. Could I ask you to please take a look at this?

[jbsauvan]

It seems there is a condition missing. It doesn't make sense to enter there if exponent==1. I will PR a fix

@jbsauvan You're the name on HGCal I know. Could I ask you to please take a look at this?

[jbsauvan]

Should be fixed in #46491