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Merge bitcoin-core/secp256k1#1438: correct assertion for secp256k1_fe_mul_inner

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dcdda31f2cda13839a4285d8601118c041b18c13 Tighten secp256k1_fe_mul_inner's VERIFY_BITS checks (Russell O'Connor)
8e2a5fe908faa2ad0b847b3e5c42662614c8fa88 correct assertion for secp256k1_fe_mul_inner (roconnor-blockstream)

Pull request description:

  Based on the surrounding asserts, 112 bits before this line, and 61 bits after this line, this assertion should be 113 bits.  Notably the commensurate line in secp256k1_fe_sqr_inner is correctly assert to be 113 bits.

ACKs for top commit:
  real-or-random:
    ACK dcdda31f2cda13839a4285d8601118c041b18c13 tested with asm disabled

Tree-SHA512: c35170e37d9a6d1413dd625032028129ab2eccee7da86697ab9641b68ad78efd7251953d51e7acaefd14888d3fd61877f9f05349c44f6fc0133ce9b3921b0e1a
This commit is contained in:
Tim Ruffing 2023-11-27 09:44:49 +01:00
commit 5814d8485c
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GPG Key ID: 8C461CCD293F6011
1 changed files with 3 additions and 3 deletions
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6
src/field_5x52_int128_impl.h
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@ -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);