// 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

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

// 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

	// vector facilities
	ve1 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 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.HasETF3Enhanced},
		{Name: "vx", Feature: &S390X.HasVX},
		{Name: "ve1", Feature: &S390X.HasVE1},
	}

	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
	}
	if S390X.HasVX {
		S390X.HasVE1 = facilities.Has(ve1)
	}
}