gfp.go

package p384

import (
	"fmt"
	"math/big"

	"golang.org/x/sys/cpu"
)

var hasBMI2 = cpu.X86.HasBMI2

type gfP [6]big.Word

func newGFp(x int64) (out *gfP) {
	if x >= 0 {
		out = &gfP{big.Word(x)}
	} else {
		out = &gfP{big.Word(-x)}
		gfpNeg(out, out)
	}

	montEncode(out, out)
	return out
}

func (e *gfP) Set(f *gfP) {
	e[0] = f[0]
	e[1] = f[1]
	e[2] = f[2]
	e[3] = f[3]
	e[4] = f[4]
	e[5] = f[5]
}

func (e *gfP) Int() *big.Int {
	return new(big.Int).SetBits(e[:])
}

func (e *gfP) String() string {
	return fmt.Sprintf("%16.16x%16.16x%16.16x%16.16x%16.16x%16.16x", e[5], e[4], e[3], e[2], e[1], e[0])
}

func (e *gfP) Invert(f *gfP) {
	bits := [6]uint64{0xfffffffd, 0xffffffff00000000, 0xfffffffffffffffe, 0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff}

	sum, power := &gfP{}, &gfP{}
	sum.Set(&rN1)
	power.Set(f)

	for word := 0; word < 6; word++ {
		for bit := uint(0); bit < 64; bit++ {
			if (bits[word]>>bit)&1 == 1 {
				gfpMul(sum, sum, power)
			}
			gfpMul(power, power, power)
		}
	}

	gfpMul(sum, sum, &r3)
	e.Set(sum)
}

func montEncode(c, a *gfP) { gfpMul(c, a, &r2) }
func montDecode(c, a *gfP) { gfpMul(c, a, &gfP{1}) }

// go:noescape
func gfpNeg(c, a *gfP)

//go:noescape
func gfpAdd(c, a, b *gfP)

//go:noescape
func gfpSub(c, a, b *gfP)

//go:noescape
func gfpMul(c, a, b *gfP)