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Merge bitcoin-core/secp256k1#943: VERIFY_CHECK precondition for secp2…
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…56k1_fe_set_int.

2888640 VERIFY_CHECK precondition for secp256k1_fe_set_int. (Russell O'Connor)
d49011f Make _set_fe_int( . , 0 ) set magnitude to 0 (Tim Ruffing)

Pull request description:

  Also set the magnitude to 0 when setting the value to 0.

ACKs for top commit:
  real-or-random:
    ACK 2888640
  jonasnick:
    ACK 2888640

Tree-SHA512: 6ec9b3485380503b11c00f30bfa79f92ba3facb93ee4f3df582b881c4e19fb8ae8b5acd5aeb6326497c290cd0904230d0356f33bd136ca577d2f25616279e090
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real-or-random committed Oct 28, 2021
2 parents 3e7b2ea + 2888640 commit 21c188b
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Showing 3 changed files with 9 additions and 5 deletions.
8 changes: 5 additions & 3 deletions src/field.h
Original file line number Diff line number Diff line change
Expand Up @@ -14,8 +14,8 @@
* - Each field element can be normalized or not.
* - Each field element has a magnitude, which represents how far away
* its representation is away from normalization. Normalized elements
* always have a magnitude of 1, but a magnitude of 1 doesn't imply
* normality.
* always have a magnitude of 0 or 1, but a magnitude of 1 doesn't
* imply normality.
*/

#if defined HAVE_CONFIG_H
Expand Down Expand Up @@ -50,7 +50,9 @@ static int secp256k1_fe_normalizes_to_zero(const secp256k1_fe *r);
* without constant-time guarantee. */
static int secp256k1_fe_normalizes_to_zero_var(const secp256k1_fe *r);

/** Set a field element equal to a small integer. Resulting field element is normalized. */
/** Set a field element equal to a small (not greater than 0x7FFF), non-negative integer.
* Resulting field element is normalized; it has magnitude 0 if a == 0, and magnitude 1 otherwise.
*/
static void secp256k1_fe_set_int(secp256k1_fe *r, int a);

/** Sets a field element equal to zero, initializing all fields. */
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3 changes: 2 additions & 1 deletion src/field_10x26_impl.h
Original file line number Diff line number Diff line change
Expand Up @@ -264,10 +264,11 @@ static int secp256k1_fe_normalizes_to_zero_var(const secp256k1_fe *r) {
}

SECP256K1_INLINE static void secp256k1_fe_set_int(secp256k1_fe *r, int a) {
VERIFY_CHECK(0 <= a && a <= 0x7FFF);
r->n[0] = 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;
#ifdef VERIFY
r->magnitude = 1;
r->magnitude = (a != 0);
r->normalized = 1;
secp256k1_fe_verify(r);
#endif
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3 changes: 2 additions & 1 deletion src/field_5x52_impl.h
Original file line number Diff line number Diff line change
Expand Up @@ -227,10 +227,11 @@ static int secp256k1_fe_normalizes_to_zero_var(const secp256k1_fe *r) {
}

SECP256K1_INLINE static void secp256k1_fe_set_int(secp256k1_fe *r, int a) {
VERIFY_CHECK(0 <= a && a <= 0x7FFF);
r->n[0] = a;
r->n[1] = r->n[2] = r->n[3] = r->n[4] = 0;
#ifdef VERIFY
r->magnitude = 1;
r->magnitude = (a != 0);
r->normalized = 1;
secp256k1_fe_verify(r);
#endif
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