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#ifndef _SECP256K1_ECMULT_
#define _SECP256K1_ECMULT_
#include <sstream>
#include <algorithm>
#include "group.h"
#include "num.h"
#define WINDOW_A 5
#define WINDOW_G 13
namespace secp256k1 {
template<typename G, int W> class WNAFPrecomp {
private:
G pre[1 << (W-2)];
public:
WNAFPrecomp() {}
void Build(const G &base) {
pre[0] = base;
GroupElemJac x(base);
GroupElemJac d; d.SetDouble(x);
for (int i=1; i<(1 << (W-2)); i++) {
x.SetAdd(d,pre[i-1]);
pre[i].SetJac(x);
}
}
WNAFPrecomp(const G &base) {
Build(base);
}
void Get(G &out, int exp) const {
assert((exp & 1) == 1);
assert(exp >= -((1 << (W-1)) - 1));
assert(exp <= ((1 << (W-1)) - 1));
if (exp > 0) {
out = pre[(exp-1)/2];
} else {
out.SetNeg(pre[(-exp-1)/2]);
}
}
};
template<int B> class WNAF {
private:
int naf[B+1];
int used;
void PushNAF(int num, int zeroes) {
assert(used < B+1);
for (int i=0; i<zeroes; i++) {
naf[used++]=0;
}
naf[used++]=num;
}
public:
WNAF(Context &ctx, const Number &exp, int w) : used(0) {
int zeroes = 0;
Context ct(ctx);
Number x(ct);
x.SetNumber(exp);
int sign = 1;
if (x.IsNeg()) {
sign = -1;
x.Negate();
}
while (!x.IsZero()) {
while (!x.IsOdd()) {
zeroes++;
x.Shift1();
}
int word = x.ShiftLowBits(ct,w);
if (word & (1 << (w-1))) {
x.Inc();
PushNAF(sign * (word - (1 << w)), zeroes);
} else {
PushNAF(sign * word, zeroes);
}
zeroes = w-1;
}
}
int GetSize() const {
return used;
}
int Get(int pos) const {
assert(pos >= 0 && pos < used);
return naf[pos];
}
std::string ToString() {
std::stringstream ss;
ss << "(";
for (int i=0; i<GetSize(); i++) {
ss << Get(used-1-i);
if (i != used-1)
ss << ',';
}
ss << ")";
return ss.str();
}
};
class ECMultConsts {
public:
WNAFPrecomp<GroupElem,WINDOW_G> wpg;
WNAFPrecomp<GroupElem,WINDOW_G> wpg128;
ECMultConsts() {
const GroupElem &g = GetGroupConst().g;
GroupElemJac g128j(g);
for (int i=0; i<128; i++)
g128j.SetDouble(g128j);
GroupElem g128; g128.SetJac(g128j);
wpg.Build(g);
wpg128.Build(g128);
}
};
const ECMultConsts &GetECMultConsts() {
static const ECMultConsts ecmult_consts;
return ecmult_consts;
}
void ECMult(Context &ctx, GroupElemJac &out, const GroupElemJac &a, const Number &an, const Number &gn) {
Context ct(ctx);
Number an1(ct), an2(ct);
Number gn1(ct), gn2(ct);
SplitExp(ct, an, an1, an2);
// printf("an=%s\n", an.ToString().c_str());
// printf("an1=%s\n", an1.ToString().c_str());
// printf("an2=%s\n", an2.ToString().c_str());
// printf("an1.len=%i\n", an1.GetBits());
// printf("an2.len=%i\n", an2.GetBits());
gn.SplitInto(ct, 128, gn1, gn2);
WNAF<129> wa1(ct, an1, WINDOW_A);
WNAF<129> wa2(ct, an2, WINDOW_A);
WNAF<128> wg1(ct, gn1, WINDOW_G);
WNAF<128> wg2(ct, gn2, WINDOW_G);
GroupElemJac a2; a2.SetMulLambda(a);
WNAFPrecomp<GroupElemJac,WINDOW_A> wpa1(a);
WNAFPrecomp<GroupElemJac,WINDOW_A> wpa2(a2);
const ECMultConsts &c = GetECMultConsts();
int size_a1 = wa1.GetSize();
int size_a2 = wa2.GetSize();
int size_g1 = wg1.GetSize();
int size_g2 = wg2.GetSize();
int size = std::max(std::max(size_a1, size_a2), std::max(size_g1, size_g2));
out = GroupElemJac();
GroupElemJac tmpj;
GroupElem tmpa;
for (int i=size-1; i>=0; i--) {
out.SetDouble(out);
int nw;
if (i < size_a1 && (nw = wa1.Get(i))) {
wpa1.Get(tmpj, nw);
out.SetAdd(out, tmpj);
}
if (i < size_a2 && (nw = wa2.Get(i))) {
wpa2.Get(tmpj, nw);
out.SetAdd(out, tmpj);
}
if (i < size_g1 && (nw = wg1.Get(i))) {
c.wpg.Get(tmpa, nw);
out.SetAdd(out, tmpa);
}
if (i < size_g2 && (nw = wg2.Get(i))) {
c.wpg128.Get(tmpa, nw);
out.SetAdd(out, tmpa);
}
}
}
}
#endif