Execution environment variables Iw and Ie

Question

According to the yellow paper, one of the Execution Environment variables is:

Iw, the permission to make modifications to the state.

I can't find further information about it, for example how it's set and what values it can get (I guess 1 or 0)

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Also I'd like to make sure that the variable

Ie, the depth of the present message-call or contract-creation (i.e. the number of CALLs or CREATEs being executed at present).

is only decremented by one for each CALL and CREATE opcodes, but never for a DELEGATECALL or CALLCODE

Answer 1

My answer is based on the current version of the yellow paper.

I_w

Iw, the permission to make modifications to the state

The importance of this flag is explained in the paragraph about Exceptional Halting:

Take into consideration only the last condition, it says that if the permission to modify is false and the current instruction is one specified by W (i.e., the instructions that may alter the state) then we have an exception. For completeness I report also the function W:

I_w is normally set to T (true) and is set to F only when a STATICCALL is performed.

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is only decremented by one for each CALL and CREATE opcodes, but never for a DELEGATECALL or CALLCODE

This is wrong. Also DELEGATECALL and CALLCODE increment and decrement the callstack (it is specified in the yellow paper).