How to calculate Tapscript sigops budget?

Question

Sigops limits have been changed to budget in Tapscript. BIP341 defines the budget calculation method as follows.

The budget equals 50 + the total serialized size in bytes of the transaction input's witness (including the CompactSize prefix). Executing a signature opcode (OP_CHECKSIG, OP_CHECKSIGVERIFY, or OP_CHECKSIGADD) with a non-empty signature decrements the budget by 50.

https://github.com/bitcoin/bips/blob/master/bip-0342.mediawiki#Resource_limits

This CompactSize prefix include the number of witness elements at the beginning?

For example, if I have the following 5 sizes of witness data,

compact size	witness size
1	65
1	64
1	91
3	257
3	563

The total size including the above Compact Size is 1049. In addition to this, do I need to add the number of bytes(1) of CompactSize for the number of elements(5)?

That's because the above data output by Bitcoin Core feature_taproot.py is 1050. The final budget will be 1100, which is 50 added to this.

Answer 1

The total size including the above Compact Size is 1049. In addition to this, do I need to add the number of bytes(1) of CompactSize for the number of elements(5)?

Indeed.

What matters is the total number of bytes of witness data for that input (i.e., all bytes subject to the witness discount). That also includes the encoding of the number of witness stack elements.