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Further performance improvements to _ecmult_wnaf

- Initialize 'wnaf' to zeroes using memset
- Add new 'len' arg to speed up smaller scalars (mostly for endo=yes)
master
Peter Dettman 7 years ago
parent
commit
55399c23f7
  1. 2
      src/bench_internal.c
  2. 49
      src/ecmult_impl.h
  3. 2
      src/tests.c

2
src/bench_internal.c

@ -229,7 +229,7 @@ void bench_ecmult_wnaf(void* arg) { @@ -229,7 +229,7 @@ void bench_ecmult_wnaf(void* arg) {
bench_inv_t *data = (bench_inv_t*)arg;
for (i = 0; i < 20000; i++) {
secp256k1_ecmult_wnaf(data->wnaf, &data->scalar_x, WINDOW_A);
secp256k1_ecmult_wnaf(data->wnaf, 256, &data->scalar_x, WINDOW_A);
secp256k1_scalar_add(&data->scalar_x, &data->scalar_x, &data->scalar_y);
}
}

49
src/ecmult_impl.h

@ -213,21 +213,28 @@ static void secp256k1_ecmult_context_clear(secp256k1_ecmult_context_t *ctx) { @@ -213,21 +213,28 @@ static void secp256k1_ecmult_context_clear(secp256k1_ecmult_context_t *ctx) {
* - each wnaf[i] is either 0, or an odd integer between -(1<<(w-1) - 1) and (1<<(w-1) - 1)
* - two non-zero entries in wnaf are separated by at least w-1 zeroes.
* - the number of set values in wnaf is returned. This number is at most 256, and at most one more
* - than the number of bits in the (absolute value) of the input.
* than the number of bits in the (absolute value) of the input.
*/
static int secp256k1_ecmult_wnaf(int *wnaf, const secp256k1_scalar_t *a, int w) {
static int secp256k1_ecmult_wnaf(int *wnaf, int len, const secp256k1_scalar_t *a, int w) {
secp256k1_scalar_t s = *a;
int set_bits = 0;
int last_set_bit = -1;
int bit = 0;
int sign = 1;
int carry = 0;
VERIFY_CHECK(wnaf != NULL);
VERIFY_CHECK(0 <= len && len <= 256);
VERIFY_CHECK(a != NULL);
VERIFY_CHECK(2 <= w && w <= 31);
memset(wnaf, 0, len * sizeof(wnaf[0]));
if (secp256k1_scalar_get_bits(&s, 255, 1)) {
secp256k1_scalar_negate(&s, &s);
sign = -1;
}
while (bit < 256) {
while (bit < len) {
int now;
int word;
if (secp256k1_scalar_get_bits(&s, bit, 1) == (unsigned int)carry) {
@ -236,8 +243,8 @@ static int secp256k1_ecmult_wnaf(int *wnaf, const secp256k1_scalar_t *a, int w) @@ -236,8 +243,8 @@ static int secp256k1_ecmult_wnaf(int *wnaf, const secp256k1_scalar_t *a, int w)
}
now = w;
if (now > 256 - bit) {
now = 256 - bit;
if (now > len - bit) {
now = len - bit;
}
word = secp256k1_scalar_get_bits_var(&s, bit, now) + carry;
@ -245,14 +252,18 @@ static int secp256k1_ecmult_wnaf(int *wnaf, const secp256k1_scalar_t *a, int w) @@ -245,14 +252,18 @@ static int secp256k1_ecmult_wnaf(int *wnaf, const secp256k1_scalar_t *a, int w)
carry = (word >> (w-1)) & 1;
word -= carry << w;
while (set_bits < bit) {
wnaf[set_bits++] = 0;
}
wnaf[set_bits++] = sign * word;
wnaf[bit] = sign * word;
last_set_bit = bit;
bit += now;
}
VERIFY_CHECK(carry == 0);
return set_bits;
#ifdef VERIFY
CHECK(carry == 0);
while (bit < 256) {
CHECK(secp256k1_scalar_get_bits(&s, bit++, 1) == 0);
}
#endif
return last_set_bit + 1;
}
static void secp256k1_ecmult(const secp256k1_ecmult_context_t *ctx, secp256k1_gej_t *r, const secp256k1_gej_t *a, const secp256k1_scalar_t *na, const secp256k1_scalar_t *ng) {
@ -275,7 +286,7 @@ static void secp256k1_ecmult(const secp256k1_ecmult_context_t *ctx, secp256k1_ge @@ -275,7 +286,7 @@ static void secp256k1_ecmult(const secp256k1_ecmult_context_t *ctx, secp256k1_ge
#else
int wnaf_na[256];
int bits_na;
int wnaf_ng[257];
int wnaf_ng[256];
int bits_ng;
#endif
int i;
@ -286,8 +297,8 @@ static void secp256k1_ecmult(const secp256k1_ecmult_context_t *ctx, secp256k1_ge @@ -286,8 +297,8 @@ static void secp256k1_ecmult(const secp256k1_ecmult_context_t *ctx, secp256k1_ge
secp256k1_scalar_split_lambda_var(&na_1, &na_lam, na);
/* build wnaf representation for na_1 and na_lam. */
bits_na_1 = secp256k1_ecmult_wnaf(wnaf_na_1, &na_1, WINDOW_A);
bits_na_lam = secp256k1_ecmult_wnaf(wnaf_na_lam, &na_lam, WINDOW_A);
bits_na_1 = secp256k1_ecmult_wnaf(wnaf_na_1, 130, &na_1, WINDOW_A);
bits_na_lam = secp256k1_ecmult_wnaf(wnaf_na_lam, 130, &na_lam, WINDOW_A);
VERIFY_CHECK(bits_na_1 <= 130);
VERIFY_CHECK(bits_na_lam <= 130);
bits = bits_na_1;
@ -296,7 +307,7 @@ static void secp256k1_ecmult(const secp256k1_ecmult_context_t *ctx, secp256k1_ge @@ -296,7 +307,7 @@ static void secp256k1_ecmult(const secp256k1_ecmult_context_t *ctx, secp256k1_ge
}
#else
/* build wnaf representation for na. */
bits_na = secp256k1_ecmult_wnaf(wnaf_na, na, WINDOW_A);
bits_na = secp256k1_ecmult_wnaf(wnaf_na, 256, na, WINDOW_A);
bits = bits_na;
#endif
@ -321,8 +332,8 @@ static void secp256k1_ecmult(const secp256k1_ecmult_context_t *ctx, secp256k1_ge @@ -321,8 +332,8 @@ static void secp256k1_ecmult(const secp256k1_ecmult_context_t *ctx, secp256k1_ge
secp256k1_scalar_split_128(&ng_1, &ng_128, ng);
/* Build wnaf representation for ng_1 and ng_128 */
bits_ng_1 = secp256k1_ecmult_wnaf(wnaf_ng_1, &ng_1, WINDOW_G);
bits_ng_128 = secp256k1_ecmult_wnaf(wnaf_ng_128, &ng_128, WINDOW_G);
bits_ng_1 = secp256k1_ecmult_wnaf(wnaf_ng_1, 129, &ng_1, WINDOW_G);
bits_ng_128 = secp256k1_ecmult_wnaf(wnaf_ng_128, 129, &ng_128, WINDOW_G);
if (bits_ng_1 > bits) {
bits = bits_ng_1;
}
@ -330,7 +341,7 @@ static void secp256k1_ecmult(const secp256k1_ecmult_context_t *ctx, secp256k1_ge @@ -330,7 +341,7 @@ static void secp256k1_ecmult(const secp256k1_ecmult_context_t *ctx, secp256k1_ge
bits = bits_ng_128;
}
#else
bits_ng = secp256k1_ecmult_wnaf(wnaf_ng, ng, WINDOW_G);
bits_ng = secp256k1_ecmult_wnaf(wnaf_ng, 256, ng, WINDOW_G);
if (bits_ng > bits) {
bits = bits_ng;
}

2
src/tests.c

@ -1374,7 +1374,7 @@ void test_wnaf(const secp256k1_scalar_t *number, int w) { @@ -1374,7 +1374,7 @@ void test_wnaf(const secp256k1_scalar_t *number, int w) {
int bits;
secp256k1_scalar_set_int(&x, 0);
secp256k1_scalar_set_int(&two, 2);
bits = secp256k1_ecmult_wnaf(wnaf, number, w);
bits = secp256k1_ecmult_wnaf(wnaf, 256, number, w);
CHECK(bits <= 256);
for (i = bits-1; i >= 0; i--) {
int v = wnaf[i];

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