// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package cpu

// bitIsSet reports whether the bit at index is set. The bit index
// is in big endian order, so bit index 0 is the leftmost bit.
func bitIsSet(bits []uint64, index uint) bool {
	return bits[index/64]&((1<<63)>>(index%64)) != 0
}

// function is the function code for the named function.
type function uint8

const (
	// KM{,A,C,CTR} function codes
	aes128 function = 18 // AES-128
	aes192 function = 19 // AES-192
	aes256 function = 20 // AES-256

	// K{I,L}MD function codes
	sha1     function = 1  // SHA-1
	sha256   function = 2  // SHA-256
	sha512   function = 3  // SHA-512
	sha3_224 function = 32 // SHA3-224
	sha3_256 function = 33 // SHA3-256
	sha3_384 function = 34 // SHA3-384
	sha3_512 function = 35 // SHA3-512
	shake128 function = 36 // SHAKE-128
	shake256 function = 37 // SHAKE-256

	// KLMD function codes
	ghash function = 65 // GHASH
)

const (
	// KDSA function codes
	ecdsaVerifyP256    function = 1  // NIST P256
	ecdsaVerifyP384    function = 2  // NIST P384
	ecdsaVerifyP521    function = 3  // NIST P521
	ecdsaSignP256      function = 9  // NIST P256
	ecdsaSignP384      function = 10 // NIST P384
	ecdsaSignP521      function = 11 // NIST P521
	eddsaVerifyEd25519 function = 32 // Curve25519
	eddsaVerifyEd448   function = 36 // Curve448
	eddsaSignEd25519   function = 40 // Curve25519
	eddsaSignEd448     function = 44 // Curve448
)

// queryResult contains the result of a Query function
// call. Bits are numbered in big endian order so the
// leftmost bit (the MSB) is at index 0.
type queryResult struct {
	bits [2]uint64
}

// Has reports whether the given functions are present.
func (q *queryResult) Has(fns ...function) bool {
	if len(fns) == 0 {
		panic("no function codes provided")
	}
	for _, f := range fns {
		if !bitIsSet(q.bits[:], uint(f)) {
			return false
		}
	}
	return true
}

// facility is a bit index for the named facility.
type facility uint8

const (
	// mandatory facilities
	zarch  facility = 1  // z architecture mode is active
	stflef facility = 7  // store-facility-list-extended
	ldisp  facility = 18 // long-displacement
	eimm   facility = 21 // extended-immediate

	// miscellaneous facilities
	dfp    facility = 42 // decimal-floating-point
	etf3eh facility = 30 // extended-translation 3 enhancement

	// cryptography facilities
	msa  facility = 17  // message-security-assist
	msa3 facility = 76  // message-security-assist extension 3
	msa4 facility = 77  // message-security-assist extension 4
	msa5 facility = 57  // message-security-assist extension 5
	msa8 facility = 146 // message-security-assist extension 8
	msa9 facility = 155 // message-security-assist extension 9

	// vector facilities
	vxe facility = 135 // vector-enhancements 1

	// Note: vx and highgprs are excluded because they require
	// kernel support and so must be fetched from HWCAP.
)

// facilityList contains the result of an STFLE call.
// Bits are numbered in big endian order so the
// leftmost bit (the MSB) is at index 0.
type facilityList struct {
	bits [4]uint64
}

// Has reports whether the given facilities are present.
func (s *facilityList) Has(fs ...facility) bool {
	if len(fs) == 0 {
		panic("no facility bits provided")
	}
	for _, f := range fs {
		if !bitIsSet(s.bits[:], uint(f)) {
			return false
		}
	}
	return true
}

// The following feature detection functions are defined in cpu_s390x.s.
// They are likely to be expensive to call so the results should be cached.
func stfle() facilityList
func kmQuery() queryResult
func kmcQuery() queryResult
func kmctrQuery() queryResult
func kmaQuery() queryResult
func kimdQuery() queryResult
func klmdQuery() queryResult
func kdsaQuery() queryResult

func doinit() {
	options = []option{
		{Name: "zarch", Feature: &S390X.HasZARCH},
		{Name: "stfle", Feature: &S390X.HasSTFLE},
		{Name: "ldisp", Feature: &S390X.HasLDISP},
		{Name: "msa", Feature: &S390X.HasMSA},
		{Name: "eimm", Feature: &S390X.HasEIMM},
		{Name: "dfp", Feature: &S390X.HasDFP},
		{Name: "etf3eh", Feature: &S390X.HasETF3EH},
		{Name: "vx", Feature: &S390X.HasVX},
		{Name: "vxe", Feature: &S390X.HasVXE},
		{Name: "kdsa", Feature: &S390X.HasKDSA},
	}

	aes := []function{aes128, aes192, aes256}
	facilities := stfle()

	if S390X.HasMSA {
		// cipher message
		km, kmc := kmQuery(), kmcQuery()
		S390X.HasAES = km.Has(aes...)
		S390X.HasAESCBC = kmc.Has(aes...)
		if facilities.Has(msa4) {
			kmctr := kmctrQuery()
			S390X.HasAESCTR = kmctr.Has(aes...)
		}
		if facilities.Has(msa8) {
			kma := kmaQuery()
			S390X.HasAESGCM = kma.Has(aes...)
		}

		// compute message digest
		kimd := kimdQuery() // intermediate (no padding)
		klmd := klmdQuery() // last (padding)
		S390X.HasSHA1 = kimd.Has(sha1) && klmd.Has(sha1)
		S390X.HasSHA256 = kimd.Has(sha256) && klmd.Has(sha256)
		S390X.HasSHA512 = kimd.Has(sha512) && klmd.Has(sha512)
		S390X.HasGHASH = kimd.Has(ghash) // KLMD-GHASH does not exist
		sha3 := []function{
			sha3_224, sha3_256, sha3_384, sha3_512,
			shake128, shake256,
		}
		S390X.HasSHA3 = kimd.Has(sha3...) && klmd.Has(sha3...)
		S390X.HasKDSA = facilities.Has(msa9) // elliptic curves
		if S390X.HasKDSA {
			kdsa := kdsaQuery()
			S390X.HasECDSA = kdsa.Has(ecdsaVerifyP256, ecdsaSignP256, ecdsaVerifyP384, ecdsaSignP384, ecdsaVerifyP521, ecdsaSignP521)
			S390X.HasEDDSA = kdsa.Has(eddsaVerifyEd25519, eddsaSignEd25519, eddsaVerifyEd448, eddsaSignEd448)
		}
	}
	if S390X.HasVX {
		S390X.HasVXE = facilities.Has(vxe)
	}
}