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Abstract out verify logic for fe_is_zero
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sipa committed May 11, 2023
1 parent c701d9a commit d3f3fe8
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Showing 4 changed files with 18 additions and 11 deletions.
10 changes: 9 additions & 1 deletion src/field.h
Original file line number Diff line number Diff line change
Expand Up @@ -82,6 +82,7 @@ static const secp256k1_fe secp256k1_const_beta = SECP256K1_FE_CONST(
# define secp256k1_fe_normalizes_to_zero_var secp256k1_fe_impl_normalizes_to_zero_var
# define secp256k1_fe_set_int secp256k1_fe_impl_set_int
# define secp256k1_fe_clear secp256k1_fe_impl_clear
# define secp256k1_fe_is_zero secp256k1_fe_impl_is_zero
#endif /* !defined(VERIFY) */

/** Normalize a field element.
Expand Down Expand Up @@ -131,7 +132,14 @@ static void secp256k1_fe_set_int(secp256k1_fe *r, int a);
*/
static void secp256k1_fe_clear(secp256k1_fe *a);

/** Verify whether a field element is zero. Requires the input to be normalized. */
/** Determine whether a represents field element 0.
*
* On input, a must be a valid normalized field element.
* Returns whether a = 0 (mod p).
*
* This behaves identical to secp256k1_normalizes_to_zero{,_var}, but requires
* normalized input (and is much faster).
*/
static int secp256k1_fe_is_zero(const secp256k1_fe *a);

/** Check the "oddness" of a field element. Requires the input to be normalized. */
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6 changes: 1 addition & 5 deletions src/field_10x26_impl.h
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Expand Up @@ -269,12 +269,8 @@ SECP256K1_INLINE static void secp256k1_fe_impl_set_int(secp256k1_fe *r, int a) {
r->n[1] = r->n[2] = r->n[3] = r->n[4] = r->n[5] = r->n[6] = r->n[7] = r->n[8] = r->n[9] = 0;
}

SECP256K1_INLINE static int secp256k1_fe_is_zero(const secp256k1_fe *a) {
SECP256K1_INLINE static int secp256k1_fe_impl_is_zero(const secp256k1_fe *a) {
const uint32_t *t = a->n;
#ifdef VERIFY
VERIFY_CHECK(a->normalized);
secp256k1_fe_verify(a);
#endif
return (t[0] | t[1] | t[2] | t[3] | t[4] | t[5] | t[6] | t[7] | t[8] | t[9]) == 0;
}

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6 changes: 1 addition & 5 deletions src/field_5x52_impl.h
Original file line number Diff line number Diff line change
Expand Up @@ -215,12 +215,8 @@ SECP256K1_INLINE static void secp256k1_fe_impl_set_int(secp256k1_fe *r, int a) {
r->n[1] = r->n[2] = r->n[3] = r->n[4] = 0;
}

SECP256K1_INLINE static int secp256k1_fe_is_zero(const secp256k1_fe *a) {
SECP256K1_INLINE static int secp256k1_fe_impl_is_zero(const secp256k1_fe *a) {
const uint64_t *t = a->n;
#ifdef VERIFY
VERIFY_CHECK(a->normalized);
secp256k1_fe_verify(a);
#endif
return (t[0] | t[1] | t[2] | t[3] | t[4]) == 0;
}

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7 changes: 7 additions & 0 deletions src/field_impl.h
Original file line number Diff line number Diff line change
Expand Up @@ -202,6 +202,13 @@ SECP256K1_INLINE static void secp256k1_fe_clear(secp256k1_fe *a) {
secp256k1_fe_impl_clear(a);
secp256k1_fe_verify(a);
}

static int secp256k1_fe_impl_is_zero(const secp256k1_fe *a);
SECP256K1_INLINE static int secp256k1_fe_is_zero(const secp256k1_fe *a) {
secp256k1_fe_verify(a);
VERIFY_CHECK(a->normalized);
return secp256k1_fe_impl_is_zero(a);
}
#endif /* defined(VERIFY) */

#endif /* SECP256K1_FIELD_IMPL_H */

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