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I notice the gas table states:

((value != 0) && (storage_location == 0)) ? 20000 : 5000

for SSTORE. What does it mean by storage_location?

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((value != 0) && (storage_location == 0)) ? 20000 : 5000

This is basically saying that it costs 20,000 gas to set any given storage location - i.e. storage slot - from 0 to value, and 5,000 gas to change its value thereafter.

So storage_location in the above will mean whichever slot in the storage we are considering.

e.g. If we are considering slot number 5 in storage, then in the above pseudo-code storage_location will be set to 5, and we are checking whether its current value is 0.


Appendix G in the Yellow Paper puts it thusly:

Gsset   20000  Paid for an SSTORE operation when the storage value is set to non-zero from zero.
Gsreset 5000   Paid for an SSTORE operation when the storage value’s zeroness remains unchanged or
is set to zero
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  • So, the gas cost of update operation is 5000, right? – chenzhongpu Apr 16 at 9:40
  • That's correct, yes. – Richard Horrocks Apr 16 at 10:22

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