Managing the stack

The following set of instructions make it possible to manage elements on the stack. They make it possible to duplicate the element at the top of the stack, remove the top element from the stack, clear the stack, swap the top two stack elements, determine the number of elements currently on the stack, copy a specified element to the top of the stack, move a specified element to the top of the stack, and rearrange the order of the top three elements on the stack.

Duplicate top stack element

DUP[ ]

Code Range	0x20
Pops	e: stack element (ULONG)
Pushes	e, e (two ULONGs)

Duplicates the element at the top of the stack.

POP top stack element

POP[ ]

Code Range	0x21
Pops	e: stack element (ULONG)
Pushes	–

Pops the top element of the stack.

Clear the entire stack

CLEAR[ ]

Code Range	0x22
Pops	all the items on the stack (ULONGs)
Pushes	–

Clears all elements from the stack.

SWAP the top two elements on the stack

SWAP[ ]

Code Range	0x23
Pops	e2: stack element (ULONG)
	e1: stack element (ULONG)
Pushes	e1, e2 (pair of ULONGs)

Swaps the top two elements of the stack making the old top element the second from the top and the old second element the top element.

Returns the DEPTH of the stack

DEPTH[ ]

Code Range	0x24
Pops	–
Pushes	n: number of elements (ULONG)

Pushes n, the number of elements currently in the stack onto the stack.

Example:

Copy the INDEXed element to the top of the stack

CINDEX[ ]

Code Range	0x25
Pops	k : stack element number
Pushes	ek: indexed element (ULONG)

Puts a copy of the kth stack element on the top of the stack.

Example:

CINDEX[ ]

Move the INDEXed element to the top of the stack

MINDEX[ ]

Code Range	0x26
Pops	k: stack element number
Pushes	e_k: indexed element

Moves the indexed element to the top of the stack.

MINDEX[ ]

ROLL the top three stack elements

ROLL[ ]

Code Range	0x8a
Pops	a, b, c (top three stack elements)
Pushes	b, a, c (elements reordered)

Performs a circular shift of the top three objects on the stack with the effect being to move the third element to the top of the stack and to move the first two elements down one position. ROLL is equivalent to MINDEX[ ] 3.