// Add(a, b, 0) -> (a, a+b, 0)
// Registers a, b and c must not overlap
// Registers a and b have the same width
// Register c is used for storing carries and must be minimum one bit wider than register a (or b)
// Initial value of c must be 0
public static void Add(this QuantumComputer comp,
Register a, Register b, Register c)
{
if (comp.Group)
{
object[] parameters = new object[] { comp, a, b, c };
comp.AddParametricGate("Add", parameters);
return;
}
else
{
comp.Group = true;
}
int width = a.Width;
int i = 0;
for (; i < width - 1; i++)
{
comp.Carry(c[i], a[i], b[i], c[i + 1]);
}
comp.Carry(c[i], a[i], b[i], b[i + 1]);
comp.CNot(b[i], a[i]);
comp.Sum(c[i], a[i], b[i]);
i--;
for (; i >= 0; i--)
{
comp.InverseCarry(c[i], a[i], b[i], c[i + 1]);
comp.Sum(c[i], a[i], b[i]);
}
}
/// <summary>
/// <para>
/// Adds two registers. The result is stored in the second. An extra register is needed for storing carry bits.
/// </para>
/// <para>
/// Add(a, b, 0) -> (a, a+b, 0)
/// </para>
/// <para>
/// In order to improve performance, this method do not check if arguments are valid.
/// They must satisfy following conditions:
/// <list type="bullet">
/// <item>Registers a, b and c must not overlap</item>
/// <item>Registers a and c must have the same width</item>
/// <item>Register b must be exactly one bit wider than register a (or c)</item>
/// <item>Initial value of c must be 0</item>
/// </list>
/// </para>
/// </summary>
/// <param name="comp">The QuantumComputer instance.</param>
/// <param name="a">The first register to sum. Its value remains unchanged.</param>
/// <param name="b">The second register to sum. After performing this operation, it contains the sum result.</param>
/// <param name="c">The extra register for storing carry bits.</param>
public static void Add(this QuantumComputer comp,
Register a, Register b, Register c)
{
int width = a.Width;
int i = 0;
for (; i < width - 1; i++)
{
comp.Carry(c[i], a[i], b[i], c[i + 1]);
}
comp.Carry(c[i], a[i], b[i], b[i + 1]);
comp.CNot(b[i], a[i]);
comp.Sum(c[i], a[i], b[i]);
i--;
for (; i >= 0; i--)
{
comp.InverseCarry(c[i], a[i], b[i], c[i + 1]);
comp.Sum(c[i], a[i], b[i]);
}
}
