# Double Numbers

This unit implements words related to handling Forth double numbers, these are,
words that are 2 cells wide.

In other Forths the signature of such words will often take a "d" parameter, in
Dusk, to emphasize their double sized nature, these will be written as "d ~"
instead, where ~ is the higher part of the number.
When talking about them the pair "dN ~" will still be written dN.

## API

dswap ( d1 ~ d2 ~ -- d2 ~ d1 ~ )
  Swap two double numbers, the equivalent of standard swap.

dnip ( d1 ~ d2 ~ -- d2 ~ )
  Remove the second highest double number from the stack.

d+ ( d1 ~ d2 ~ -- d ~ )
  Compute the sum of d1 with d2, taking care of carry across word boundaries.

d- ( d1 ~ d2 ~ -- d ~ )
  Return the substraction of d1 by d2, this function also handles carries.

dneg ( d ~ -- d ~ )
  Negate the double number d1 returning d2.

n>d ( n -- d ~ )
  Convert a standard number to a double number.

d>n ( d ~ -- n )
  Convert a double number to a standard number, this is currently an alias to
  drop.

d2/ ( d ~ -- d ~ )
  Divide the double number by 2, equivalent to shifting by 1 bit to the right.

d2* ( d ~ -- d ~ )
  Multiply the double number by 2, equivalent to shifting by 1 bit to the left.

d= ( d1 ~ d2 ~ -- f )
  Test for equality between d1 and d2, returning true if they are equal.