// 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     { panic("not implemented for gccgo") }
func kmQuery() queryResult    { panic("not implemented for gccgo") }
func kmcQuery() queryResult   { panic("not implemented for gccgo") }
func kmctrQuery() queryResult { panic("not implemented for gccgo") }
func kmaQuery() queryResult   { panic("not implemented for gccgo") }
func kimdQuery() queryResult  { panic("not implemented for gccgo") }
func klmdQuery() queryResult  { panic("not implemented for gccgo") }

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()

	S390X.HasZArch = facilities.Has(zarch)
	S390X.HasSTFLE = facilities.Has(stflef)
	S390X.HasLDisp = facilities.Has(ldisp)
	S390X.HasEImm = facilities.Has(eimm)
	S390X.HasDFP = facilities.Has(dfp)
	S390X.HasETF3Enhanced = facilities.Has(etf3eh)
	S390X.HasMSA = facilities.Has(msa)

	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)
	}
}