package sike

// Helpers

// uint128 representation
type uint128 struct {
	H, L uint64
}

func addc64(cin, a, b uint64) (ret, cout uint64) {
	ret = cin
	ret = ret + a
	if ret < a {
		cout = 1
	}
	ret = ret + b
	if ret < b {
		cout = 1
	}

	return
}

func subc64(bIn, a, b uint64) (ret, bOut uint64) {
	tmp := a - bIn
	if tmp > a {
		bOut = 1
	}
	ret = tmp - b
	if ret > tmp {
		bOut = 1
	}
	return
}

func mul64(a, b uint64) (res uint128) {
	var al, bl, ah, bh, albl, albh, ahbl, ahbh uint64
	var res1, res2, res3 uint64
	var carry, maskL, maskH, temp uint64

	maskL = (^maskL) >> 32
	maskH = ^maskL

	al = a & maskL
	ah = a >> 32
	bl = b & maskL
	bh = b >> 32

	albl = al * bl
	albh = al * bh
	ahbl = ah * bl
	ahbh = ah * bh
	res.L = albl & maskL

	res1 = albl >> 32
	res2 = ahbl & maskL
	res3 = albh & maskL
	temp = res1 + res2 + res3
	carry = temp >> 32
	res.L ^= temp << 32

	res1 = ahbl >> 32
	res2 = albh >> 32
	res3 = ahbh & maskL
	temp = res1 + res2 + res3 + carry
	res.H = temp & maskL
	carry = temp & maskH
	res.H ^= (ahbh & maskH) + carry
	return
}