Skip to content

Commit

Permalink
Add IsSquare method + small CMov bugfix
Browse files Browse the repository at this point in the history
  • Loading branch information
@Coding-Enthusiast
Coding-Enthusiast committed Dec 26, 2023
1 parent 18c79d1 commit 2f7e898
Showing 1 changed file with 83 additions and 24 deletions.
107 changes: 83 additions & 24 deletions Src/Autarkysoft.Bitcoin/Cryptography/EllipticCurve/UInt256_10x26.cs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -138,9 +138,9 @@ public UInt256_10x26(ReadOnlySpan<uint> arr10
/// </summary>
/// <param name="ba32">32-byte array</param>
/// <param name="isValid"></param>
[Obsolete]
public UInt256_10x26(ReadOnlySpan<byte> ba32, out bool isValid)
{
// This is the same as secp256k1_fe_impl_set_b32_limit
Debug.Assert(ba32.Length == 32);

// 8 + 8 + 8 + 2
Expand Down Expand Up @@ -177,44 +177,66 @@ public UInt256_10x26(ReadOnlySpan<byte> ba32, out bool isValid)
}


public static UInt256_10x26 SetB32Mod(ReadOnlySpan<byte> ba32)
public UInt256_10x26(ReadOnlySpan<byte> ba32)
{
// This is the same as secp256k1_fe_impl_set_b32_mod
Debug.Assert(ba32.Length == 32);

// 8 + 8 + 8 + 2
uint u0 = (uint)(ba32[31] | (ba32[30] << 8) | (ba32[29] << 16) | ((ba32[28] & 0b00000011) << 24));
b0 = (uint)(ba32[31] | (ba32[30] << 8) | (ba32[29] << 16) | ((ba32[28] & 0b00000011) << 24));
// 6 + 8 + 8 + 4
uint u1 = (uint)((ba32[28] >> 2) | (ba32[27] << 6) | (ba32[26] << 14) | ((ba32[25] & 0b00001111) << 22));
b1 = (uint)((ba32[28] >> 2) | (ba32[27] << 6) | (ba32[26] << 14) | ((ba32[25] & 0b00001111) << 22));
// 4 + 8 + 8 + 6
uint u2 = (uint)((ba32[25] >> 4) | (ba32[24] << 4) | (ba32[23] << 12) | ((ba32[22] & 0b00111111) << 20));
b2 = (uint)((ba32[25] >> 4) | (ba32[24] << 4) | (ba32[23] << 12) | ((ba32[22] & 0b00111111) << 20));
// 2 + 8 + 8 + 8
uint u3 = (uint)((ba32[22] >> 6) | (ba32[21] << 2) | (ba32[20] << 10) | (ba32[19] << 18));
b3 = (uint)((ba32[22] >> 6) | (ba32[21] << 2) | (ba32[20] << 10) | (ba32[19] << 18));
// 8 + 8 + 8 + 2
uint u4 = (uint)(ba32[18] | (ba32[17] << 8) | (ba32[16] << 16) | ((ba32[15] & 0b00000011) << 24));
b4 = (uint)(ba32[18] | (ba32[17] << 8) | (ba32[16] << 16) | ((ba32[15] & 0b00000011) << 24));
// 6 + 8 + 8 + 4
uint u5 = (uint)((ba32[15] >> 2) | (ba32[14] << 6) | (ba32[13] << 14) | ((ba32[12] & 0b00001111) << 22));
b5 = (uint)((ba32[15] >> 2) | (ba32[14] << 6) | (ba32[13] << 14) | ((ba32[12] & 0b00001111) << 22));
// 4 + 8 + 8 + 6
uint u6 = (uint)((ba32[12] >> 4) | (ba32[11] << 4) | (ba32[10] << 12) | ((ba32[9] & 0b00111111) << 20));
b6 = (uint)((ba32[12] >> 4) | (ba32[11] << 4) | (ba32[10] << 12) | ((ba32[9] & 0b00111111) << 20));
// 2 + 8 + 8 + 8
uint u7 = (uint)((ba32[9] >> 6) | (ba32[8] << 2) | (ba32[7] << 10) | (ba32[6] << 18));
b7 = (uint)((ba32[9] >> 6) | (ba32[8] << 2) | (ba32[7] << 10) | (ba32[6] << 18));
// 8 + 8 + 8 + 2
uint u8 = (uint)(ba32[5] | (ba32[4] << 8) | (ba32[3] << 16) | ((ba32[2] & 0b00000011) << 24));
b8 = (uint)(ba32[5] | (ba32[4] << 8) | (ba32[3] << 16) | ((ba32[2] & 0b00000011) << 24));
// 6 + 8 + 8 (last item is only 22 bits)
uint u9 = (uint)((ba32[2] >> 2) | (ba32[1] << 6) | (ba32[0] << 14));

return new UInt256_10x26(u0, u1, u2, u3, u4, u5, u6, u7, u8, u9
b9 = (uint)((ba32[2] >> 2) | (ba32[1] << 6) | (ba32[0] << 14));
#if DEBUG
, 1, false
magnitude = 1;
isNormalized = false;
#endif
);
}

public static UInt256_10x26 SetB32Limit(ReadOnlySpan<byte> ba32, out bool isValid)
{
UInt256_10x26 r = SetB32Mod(ba32);
isValid = !((r.b9 == 0x003FFFFFU) & ((r.b8 & r.b7 & r.b6 & r.b5 & r.b4 & r.b3 & r.b2) == 0x03FFFFFFU) &
((r.b1 + 0x40U + ((r.b0 + 0x03D1U) >> 26)) > 0x03FFFFFFU));

/// <summary>
/// Return a field element with magnitude m, normalized if (and only if) m==0.
/// The value is chosen so that it is likely to trigger edge cases related to
/// internal overflows.
/// </summary>
public static UInt256_10x26 GetBounds(uint m)
{
Debug.Assert(m >= 0);
Debug.Assert(m <= 32);

UInt256_10x26 r = new UInt256_10x26(
0x3FFFFFFU * 2 * m,
0x3FFFFFFU * 2 * m,
0x3FFFFFFU * 2 * m,
0x3FFFFFFU * 2 * m,
0x3FFFFFFU * 2 * m,
0x3FFFFFFU * 2 * m,
0x3FFFFFFU * 2 * m,
0x3FFFFFFU * 2 * m,
0x3FFFFFFU * 2 * m,
0x03FFFFFU * 2 * m
#if DEBUG
, (int)m, m == 0
#endif
);
#if DEBUG
r.Verify();
#endif
return r;
}

Expand All @@ -223,6 +245,7 @@ public static UInt256_10x26 SetB32Limit(ReadOnlySpan<byte> ba32, out bool isVali
/// Bit chunks
/// </summary>
public readonly uint b0, b1, b2, b3, b4, b5, b6, b7, b8, b9;

#if DEBUG
/// <summary>
/// Magnitude means:
Expand Down Expand Up @@ -1264,6 +1287,43 @@ public UInt256_10x26 Negate(int m)
}


/// <summary>
/// Determine whether this is a square (modulo p).
/// </summary>
/// <returns></returns>
public bool IsSquareVar()
{
#if DEBUG
Verify();
#endif
bool ret;
UInt256_10x26 tmp = NormalizeVar();
// secp256k1_jacobi32_maybe_var cannot deal with input 0.
if (tmp.IsZero)
{
ret = true;
}

ModInv32Signed30 s = new ModInv32Signed30(tmp);
int jac = ModInv32.Jacobi32MaybeVar(s, ModInv32ModInfo.FeConstant);
if (jac == 0)
{
// secp256k1_jacobi32_maybe_var failed to compute the Jacobi symbol. Fall back
// to computing a square root. This should be extremely rare with random
// input (except in VERIFY mode, where a lower iteration count is used).
ret = Sqrt(out _);
}
else
{
ret = jac >= 0;
}
#if DEBUG
tmp = NormalizeWeak();
Debug.Assert(ret == tmp.Sqrt(out _));
#endif
return ret;
}

/// <summary>
/// Returns square (x^2 or x*x) of this instance.
/// </summary>
Expand Down Expand Up @@ -1664,7 +1724,6 @@ public bool Sqrt(out UInt256_10x26 result)
/// <returns></returns>
public UInt256_10x26 InverseVariable_old()
{
// TODO: complete these implementations
return Inverse_old();
}

Expand Down Expand Up @@ -1774,8 +1833,8 @@ public static UInt256_10x26 CMov(in UInt256_10x26 r, in UInt256_10x26 a, uint fl
(r.b8 & mask0) | (a.b8 & mask1),
(r.b9 & mask0) | (a.b9 & mask1)
#if DEBUG
, flag != 0 ? a.magnitude : r.magnitude,
flag != 0 ? a.isNormalized : r.isNormalized
, a.magnitude > r.magnitude ? a.magnitude : r.magnitude,
!a.isNormalized ? false : r.isNormalized
#endif
);
}
Expand Down

0 comments on commit 2f7e898

Please sign in to comment.