Add support for EIP-1087: Net storage gas metering for the EVM

[chfast]

I propose to extend the function evmc_set_storage() by returning additional information to

enum evmc_storage_status evmc_set_storage(
    struct evmc_context* context,
    const struct evmc_address* address,
    const struct evmc_uint256be* key,
    const struct evmc_uint256be* value
);

The enum evmc_storage_status would contain the information what happened with the storage, like

• unmodified,
• modified,
• added,
• deleted,
• modified_dirty.

The gas cost is going to be applied after the evmc_set_storage() is executed (is this a problem?).

This also avoids calling evmc_get_storage() first.

[chfast]

cc @Arachnid

[gumb0]

The EIP suggests different costs when the slot is modified for the first time in transaction vs subsequent modification in the same transaction, so I think this proposal doesn't cover this difference.

[chfast]

The EIP suggessts different costs when the slot is modified for the first time in transaction vs subsequent modification in the same transaction, so I think this proposal doesn't cover this difference.

You are right. I didn't wanted to make it so much detailed. I meant "include any distinctive storage status need to implement Constantinople".

I added modified_dirty status which means "a dirty storage slot was modified".

[gumb0]

Sufficient statuses I think would be

• unmodified
• added_clear // modified for the first time the slot that was zero
• modified_clear // modified for the first time the slot that was non-zero
• modified_dirty

(Refunds for deleting are handled outside of VM in transaction finalization)

[chfast]

I will work on this.

[chfast]

I'm closing it as partly done in #52. The list would have to extended for EIP-1087, but nothing complicated is expected.