github.com/deroproject/derosuite@v2.1.6-1.0.20200307070847-0f2e589c7a2b+incompatible/crypto/edwards25519_field.go

// Copyright 2016 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 crypto

// This file contains field element logic that is independent of the
// representation.

var zero FieldElement

func load3(in []byte) int64 {
	var r int64
	r = int64(in[0])
	r |= int64(in[1]) << 8
	r |= int64(in[2]) << 16
	return r
}

func load4(in []byte) int64 {
	var r int64
	r = int64(in[0])
	r |= int64(in[1]) << 8
	r |= int64(in[2]) << 16
	r |= int64(in[3]) << 24
	return r
}

func FeZero(fe *FieldElement) {
	copy(fe[:], zero[:])
}

func FeOne(fe *FieldElement) {
	FeZero(fe)
	fe[0] = 1
}

func FeCopy(dst, src *FieldElement) {
	copy(dst[:], src[:])
}

func FeIsNegative(f *FieldElement) byte {
	var s Key
	FeToBytes(&s, f)
	return s[0] & 1
}

func FeIsNonZero(f *FieldElement) int32 {
	var s Key
	FeToBytes(&s, f)
	var x uint8
	for _, b := range s {
		x |= b
	}
	x |= x >> 4
	x |= x >> 2
	x |= x >> 1
	return int32(x & 1)
}

func FeInvert(out, z *FieldElement) {
	var t0, t1, t2, t3 FieldElement
	var i int

	FeSquare(&t0, z)        // 2^1
	FeSquare(&t1, &t0)      // 2^2
	for i = 1; i < 2; i++ { // 2^3
		FeSquare(&t1, &t1)
	}
	FeMul(&t1, z, &t1)      // 2^3 + 2^0
	FeMul(&t0, &t0, &t1)    // 2^3 + 2^1 + 2^0
	FeSquare(&t2, &t0)      // 2^4 + 2^2 + 2^1
	FeMul(&t1, &t1, &t2)    // 2^4 + 2^3 + 2^2 + 2^1 + 2^0
	FeSquare(&t2, &t1)      // 5,4,3,2,1
	for i = 1; i < 5; i++ { // 9,8,7,6,5
		FeSquare(&t2, &t2)
	}
	FeMul(&t1, &t2, &t1)     // 9,8,7,6,5,4,3,2,1,0
	FeSquare(&t2, &t1)       // 10..1
	for i = 1; i < 10; i++ { // 19..10
		FeSquare(&t2, &t2)
	}
	FeMul(&t2, &t2, &t1)     // 19..0
	FeSquare(&t3, &t2)       // 20..1
	for i = 1; i < 20; i++ { // 39..20
		FeSquare(&t3, &t3)
	}
	FeMul(&t2, &t3, &t2)     // 39..0
	FeSquare(&t2, &t2)       // 40..1
	for i = 1; i < 10; i++ { // 49..10
		FeSquare(&t2, &t2)
	}
	FeMul(&t1, &t2, &t1)     // 49..0
	FeSquare(&t2, &t1)       // 50..1
	for i = 1; i < 50; i++ { // 99..50
		FeSquare(&t2, &t2)
	}
	FeMul(&t2, &t2, &t1)      // 99..0
	FeSquare(&t3, &t2)        // 100..1
	for i = 1; i < 100; i++ { // 199..100
		FeSquare(&t3, &t3)
	}
	FeMul(&t2, &t3, &t2)     // 199..0
	FeSquare(&t2, &t2)       // 200..1
	for i = 1; i < 50; i++ { // 249..50
		FeSquare(&t2, &t2)
	}
	FeMul(&t1, &t2, &t1)    // 249..0
	FeSquare(&t1, &t1)      // 250..1
	for i = 1; i < 5; i++ { // 254..5
		FeSquare(&t1, &t1)
	}
	FeMul(out, &t1, &t0) // 254..5,3,1,0
}

func fePow22523(out, z *FieldElement) {
	var t0, t1, t2 FieldElement
	var i int

	FeSquare(&t0, z)
	for i = 1; i < 1; i++ {
		FeSquare(&t0, &t0)
	}
	FeSquare(&t1, &t0)
	for i = 1; i < 2; i++ {
		FeSquare(&t1, &t1)
	}
	FeMul(&t1, z, &t1)
	FeMul(&t0, &t0, &t1)
	FeSquare(&t0, &t0)
	for i = 1; i < 1; i++ {
		FeSquare(&t0, &t0)
	}
	FeMul(&t0, &t1, &t0)
	FeSquare(&t1, &t0)
	for i = 1; i < 5; i++ {
		FeSquare(&t1, &t1)
	}
	FeMul(&t0, &t1, &t0)
	FeSquare(&t1, &t0)
	for i = 1; i < 10; i++ {
		FeSquare(&t1, &t1)
	}
	FeMul(&t1, &t1, &t0)
	FeSquare(&t2, &t1)
	for i = 1; i < 20; i++ {
		FeSquare(&t2, &t2)
	}
	FeMul(&t1, &t2, &t1)
	FeSquare(&t1, &t1)
	for i = 1; i < 10; i++ {
		FeSquare(&t1, &t1)
	}
	FeMul(&t0, &t1, &t0)
	FeSquare(&t1, &t0)
	for i = 1; i < 50; i++ {
		FeSquare(&t1, &t1)
	}
	FeMul(&t1, &t1, &t0)
	FeSquare(&t2, &t1)
	for i = 1; i < 100; i++ {
		FeSquare(&t2, &t2)
	}
	FeMul(&t1, &t2, &t1)
	FeSquare(&t1, &t1)
	for i = 1; i < 50; i++ {
		FeSquare(&t1, &t1)
	}
	FeMul(&t0, &t1, &t0)
	FeSquare(&t0, &t0)
	for i = 1; i < 2; i++ {
		FeSquare(&t0, &t0)
	}
	FeMul(out, &t0, z)
}