how to calculate p2wsh signature?

[wujing2019]

I read bip 143, it told us how to calculate p2wsh signature:
A new transaction digest algorithm is defined, but only applicable to sigops in version 0 witness program
Double SHA256 of the serialization of:
1. nVersion of the transaction (4-byte little endian)
2. hashPrevouts (32-byte hash)
3. hashSequence (32-byte hash)
4. outpoint (32-byte hash + 4-byte little endian)
5. scriptCode of the input (serialized as scripts inside CTxOuts)
6. value of the output spent by this input (8-byte little endian)
7. nSequence of the input (4-byte little endian)
8. hashOutputs (32-byte hash)
9. nLocktime of the transaction (4-byte little endian)
10. sighash type of the signature (4-byte little endian)

The item 5:

For P2WPKH witness program, the scriptCode is 0x1976a914{20-byte-pubkey-hash}88ac.
For P2WSH witness program,
if the witnessScript does not contain any OP_CODESEPARATOR, the scriptCode is the witnessScript serialized as scripts inside CTxOut.
if the witnessScript contains any OP_CODESEPARATOR, the scriptCode is the witnessScript but removing everything up to and including the last executed OP_CODESEPARATOR before the signature checking opcode being executed, serialized as scripts inside CTxOut. (The exact semantics is demonstrated in the examples below)

I didn't understand the description about how to calculate scriptCode above, so I found out the function "calcWitnessSignatureHash" and saw the code below:

if isWitnessPubKeyHash(subScript) {
	// The script code for a p2wkh is a length prefix varint for
	// the next 25 bytes, followed by a re-creation of the original
	// p2pkh pk script.
	sigHash.Write([]byte{0x19})
	sigHash.Write([]byte{OP_DUP})
	sigHash.Write([]byte{OP_HASH160})
	sigHash.Write([]byte{OP_DATA_20})
	sigHash.Write(subScript[1].data)
	sigHash.Write([]byte{OP_EQUALVERIFY})
	sigHash.Write([]byte{OP_CHECKSIG})
} else {
	// For p2wsh outputs, and future outputs, the script code is
	// the original script, with all code separators removed,
	// serialized with a var int length prefix.
	rawScript, _ := unparseScript(subScript)
	wire.WriteVarBytes(&sigHash, 0, rawScript)
}

It seems different from the discription in bip143.
Did btcd implement the discription of "For P2WSH witness program..." in bip143?
If did, which function I could find the logic?
thanks a lot.