1package x25519
 2
 3import (
 4	"encoding/binary"
 5	"math/bits"
 6
 7	fp "github.com/cloudflare/circl/math/fp25519"
 8)
 9
10func doubleGeneric(x, z *fp.Elt) {
11	t0, t1 := &fp.Elt{}, &fp.Elt{}
12	fp.AddSub(x, z)
13	fp.Sqr(x, x)
14	fp.Sqr(z, z)
15	fp.Sub(t0, x, z)
16	mulA24Generic(t1, t0)
17	fp.Add(t1, t1, z)
18	fp.Mul(x, x, z)
19	fp.Mul(z, t0, t1)
20}
21
22func diffAddGeneric(w *[5]fp.Elt, b uint) {
23	mu, x1, z1, x2, z2 := &w[0], &w[1], &w[2], &w[3], &w[4]
24	fp.Cswap(x1, x2, b)
25	fp.Cswap(z1, z2, b)
26	fp.AddSub(x1, z1)
27	fp.Mul(z1, z1, mu)
28	fp.AddSub(x1, z1)
29	fp.Sqr(x1, x1)
30	fp.Sqr(z1, z1)
31	fp.Mul(x1, x1, z2)
32	fp.Mul(z1, z1, x2)
33}
34
35func ladderStepGeneric(w *[5]fp.Elt, b uint) {
36	x1, x2, z2, x3, z3 := &w[0], &w[1], &w[2], &w[3], &w[4]
37	t0 := &fp.Elt{}
38	t1 := &fp.Elt{}
39	fp.AddSub(x2, z2)
40	fp.AddSub(x3, z3)
41	fp.Mul(t0, x2, z3)
42	fp.Mul(t1, x3, z2)
43	fp.AddSub(t0, t1)
44	fp.Cmov(x2, x3, b)
45	fp.Cmov(z2, z3, b)
46	fp.Sqr(x3, t0)
47	fp.Sqr(z3, t1)
48	fp.Mul(z3, x1, z3)
49	fp.Sqr(x2, x2)
50	fp.Sqr(z2, z2)
51	fp.Sub(t0, x2, z2)
52	mulA24Generic(t1, t0)
53	fp.Add(t1, t1, z2)
54	fp.Mul(x2, x2, z2)
55	fp.Mul(z2, t0, t1)
56}
57
58func mulA24Generic(z, x *fp.Elt) {
59	const A24 = 121666
60	const n = 8
61	var xx [4]uint64
62	for i := range xx {
63		xx[i] = binary.LittleEndian.Uint64(x[i*n : (i+1)*n])
64	}
65
66	h0, l0 := bits.Mul64(xx[0], A24)
67	h1, l1 := bits.Mul64(xx[1], A24)
68	h2, l2 := bits.Mul64(xx[2], A24)
69	h3, l3 := bits.Mul64(xx[3], A24)
70
71	var c3 uint64
72	l1, c0 := bits.Add64(h0, l1, 0)
73	l2, c1 := bits.Add64(h1, l2, c0)
74	l3, c2 := bits.Add64(h2, l3, c1)
75	l4, _ := bits.Add64(h3, 0, c2)
76	_, l4 = bits.Mul64(l4, 38)
77	l0, c0 = bits.Add64(l0, l4, 0)
78	xx[1], c1 = bits.Add64(l1, 0, c0)
79	xx[2], c2 = bits.Add64(l2, 0, c1)
80	xx[3], c3 = bits.Add64(l3, 0, c2)
81	xx[0], _ = bits.Add64(l0, (-c3)&38, 0)
82	for i := range xx {
83		binary.LittleEndian.PutUint64(z[i*n:(i+1)*n], xx[i])
84	}
85}