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Improve perf. of cmov-based table lookup

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Peter Dettman 2015-07-15 20:33:35 +07:00 • committed by Andrew Poelstra
parent 92e53fc4c8
commit 72ae443afb
2 changed files with 11 additions and 5 deletions
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14
src/ecmult_const_impl.h
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@ -23,19 +23,20 @@
#define ECMULT_CONST_TABLE_GET_GE(r,pre,n,w) do { \
int m; \
int abs_n = (n) * (((n) > 0) * 2 - 1); \
int idx_n = abs_n / 2; \
secp256k1_fe_t neg_y; \
VERIFY_CHECK(((n) & 1) == 1); \
VERIFY_CHECK((n) >= -((1 << ((w)-1)) - 1)); \
VERIFY_CHECK((n) <= ((1 << ((w)-1)) - 1)); \
for (m = 1; m < (1 << ((w) - 1)); m += 2) { \
VERIFY_SETUP(secp256k1_fe_clear(&(r)->x)); \
VERIFY_SETUP(secp256k1_fe_clear(&(r)->y)); \
for (m = 0; m < ECMULT_TABLE_SIZE(w); m++) { \
/* This loop is used to avoid secret data in array indices. See
* the comment in ecmult_gen_impl.h for rationale. */ \
secp256k1_fe_cmov(&(r)->x, &(pre)[(m - 1) / 2].x, m == abs_n); \
secp256k1_fe_cmov(&(r)->y, &(pre)[(m - 1) / 2].y, m == abs_n); \
secp256k1_fe_cmov(&(r)->x, &(pre)[m].x, m == idx_n); \
secp256k1_fe_cmov(&(r)->y, &(pre)[m].y, m == idx_n); \
} \
(r)->infinity = 0; \
secp256k1_fe_normalize_weak(&(r)->x); \
secp256k1_fe_normalize_weak(&(r)->y); \
secp256k1_fe_negate(&neg_y, &(r)->y, 1); \
secp256k1_fe_cmov(&(r)->y, &neg_y, (n) != abs_n); \
} while(0)
@ -164,6 +165,9 @@ static void secp256k1_ecmult_const(secp256k1_gej_t *r, const secp256k1_ge_t *a,
*/
secp256k1_gej_set_ge(r, a);
secp256k1_ecmult_odd_multiples_table_globalz_windowa(pre_a, &Z, r);
for (i = 0; i < ECMULT_TABLE_SIZE(WINDOW_A); i++) {
secp256k1_fe_normalize_weak(&pre_a[i].y);
}
#ifdef USE_ENDOMORPHISM
for (i = 0; i < ECMULT_TABLE_SIZE(WINDOW_A); i++) {
secp256k1_ge_mul_lambda(&pre_a_lam[i], &pre_a[i]);

2
src/util.h
View file

@ -55,8 +55,10 @@ typedef struct {
/* Like assert(), but when VERIFY is defined, and side-effect safe. */
#ifdef VERIFY
#define VERIFY_CHECK CHECK
#define VERIFY_SETUP(stmt) do { stmt; } while(0)
#else
#define VERIFY_CHECK(cond) do { (void)(cond); } while(0)
#define VERIFY_SETUP(stmt)
#endif
static SECP256K1_INLINE void *checked_malloc(const callback_t* cb, size_t size) {