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correct assertion for secp256k1_fe_mul_inner #1438

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Merged
merged 2 commits into from
Nov 27, 2023
Merged

correct assertion for secp256k1_fe_mul_inner #1438

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8e2a5fe
correct assertion for secp256k1_fe_mul_inner
roconnor-blockstream Nov 6, 2023
dcdda31
Tighten secp256k1_fe_mul_inner's VERIFY_BITS checks
roconnor-blockstream Nov 14, 2023
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6 changes: 3 additions & 3 deletions src/field_5x52_int128_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -89,18 +89,18 @@ SECP256K1_INLINE static void secp256k1_fe_mul_inner(uint64_t *r, const uint64_t
secp256k1_u128_accum_mul(&d, a2, b[3]);
secp256k1_u128_accum_mul(&d, a3, b[2]);
secp256k1_u128_accum_mul(&d, a4, b[1]);
VERIFY_BITS_128(&d, 115);
VERIFY_BITS_128(&d, 114);
/* [d t4+(tx<<48) t3 0 0 c] = [p8 0 0 p5 p4 p3 0 0 p0] */
u0 = secp256k1_u128_to_u64(&d) & M; secp256k1_u128_rshift(&d, 52);
VERIFY_BITS(u0, 52);
VERIFY_BITS_128(&d, 63);
VERIFY_BITS_128(&d, 62);
/* [d u0 t4+(tx<<48) t3 0 0 c] = [p8 0 0 p5 p4 p3 0 0 p0] */
/* [d 0 t4+(tx<<48)+(u0<<52) t3 0 0 c] = [p8 0 0 p5 p4 p3 0 0 p0] */
u0 = (u0 << 4) | tx;
VERIFY_BITS(u0, 56);
/* [d 0 t4+(u0<<48) t3 0 0 c] = [p8 0 0 p5 p4 p3 0 0 p0] */
secp256k1_u128_accum_mul(&c, u0, R >> 4);
VERIFY_BITS_128(&c, 115);
VERIFY_BITS_128(&c, 113);
/* [d 0 t4 t3 0 0 c] = [p8 0 0 p5 p4 p3 0 0 p0] */
r[0] = secp256k1_u128_to_u64(&c) & M; secp256k1_u128_rshift(&c, 52);
VERIFY_BITS(r[0], 52);
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