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Zero VM Instruction Set Architecture (ISA) Reference

This document provides a technical specification for the Zero VM assembly instructions. The Virtual Machine operates on a Stack-Based Architecture where most instructions pop operands from the top of the stack and push results back.

1. Memory Operations

STORE

Description: Pops the top value from the stack and stores it in a specified location.

  • STORE <index>: Pops the value and stores it at the absolute stack index.
  • STORE [*]: Pops the value into the ei (Return Value) register.
  • STORE #<offset>: Pops the value and stores it at the relative position bp + offset (Base Pointer offset).

LOAD

Description: Loads a value from a specified location and pushes it onto the stack.

  • LOAD <index>: Loads data from the absolute stack index.
  • LOAD [*]: Loads data from the ei register.
  • LOAD #<offset>: Loads data from the relative position bp + offset.
  • LOAD .<name>: Loads the function pointer associated with name from the Symbol Table.

2. Immediate Constants (Push Operations)

These instructions push literal values of specific types onto the stack.

Instruction Type Example Description
PUSH_D Integer PUSH_D 1 Push a 64-bit integer.
PUSH_F Float PUSH_F 1.2 Push a double-precision floating point.
PUSH_B Boolean PUSH_B 1 Push true (1) or false (0).
PUSH_S String PUSH_S "text" Push a string constant.
PUSH_N Null PUSH_N Push a null value.

3. Function Calls & Stack Management

CALL

Description: Transfers control to a function.

  • CALL <name>: Calls the function by its identifier.
  • CALL -1: Dynamic call. Pops the value at top - 1 and treats it as a function pointer to execute.

FREE

Description: Cleans up the stack.

  • FREE <n>: Removes n elements from the top of the stack.

GET

Description: Property access for objects.

  • Pops a (attribute name) and b (object).
  • Pushes the value of b.a onto the stack. Requires b to be an Object type.

SET

Description: Property set for objects.

  • Pops a (attribute name) and b (object) and c (value).
  • Set c to a.b.

ASSIGN

Description: Direct assignment.

  • Pops value a. Assigns it to the element at top - 1.
  • Requirement: The element at top - 1 must be a reference type.

4. Arithmetic & Logical Instructions

Unless otherwise specified, these instructions pop two values: a (top) and b (top-1), then push the result of b [op] a.

Mnemonic Operation Description
ADD b + a Addition.
MINUS b - a Subtraction.
MULTI b * a Multiplication.
DIV b / a Division.
NEGATE -a Pops a, pushes its arithmetic negation.

Comparison

  • G / GE: Greater Than (b > a) / Greater or Equal (b >= a).
  • L / LE: Less Than (b < a) / Less or Equal (b <= a).
  • E / NE: Equal (b == a) / Not Equal (b != a).
  • NOT: Logical NOT (!a). Pops a, pushes inverted boolean result.

5. Control Flow (Branching)

JUMP

Description: Unconditional relative jump.

  • JUMP <offset>: Moves the Program Counter (PC) by the specified offset (e.g., PC = PC + offset).

JF (Jump if False)

Description: Conditional relative jump.

  • Pops the top value. If it is false, PC = PC + offset. Otherwise, proceeds to the next instruction.