wassembly/design.md

Design

Parsing

• First we tokenize the input (syntax check)
• Then we interpret the input (semantics check)
• Then we execute the input

Notation

• [operation][number type], e.g. divi for divide (div) integer
• %[register] for addressing registers
• $[value] for using literals/immediate values
• ; for end of statement (mandatory)
• [label]: for labels
• #[text] for comments: any text is ignored till a newline (\n) is found
• Elements must be separated by whitespace character
  • Good: add $2 $5 %A;
  • Bad: add $2$5%A;

Examples

Divide register A by 5 and store the result in register A: divi %A $5 %A;

Increment B until it is 10:

# Set B to zero
addi $0 $0 %B;

loop:
addi $1 %B %B;
lti %B $10;
jmp loop;

Reserved symbols

The following whitespace characters are used to separate symbols:

• space ( )
• tab (\t)
• return carriage (\r)
• newline (\n)

The following characters are used as identifiers:

• dollar ($) for immediate (literal) values
• percentage (%) for register identifiers
• colon (:) for jump labels
• semicolon (;) for statement termination
• hash (#) for comments

All symbols are reserved keywords and can therefore NOT be used as labels.

Symbols

Operands

• addi add the first to the second argument and store the result in the third argument
• subi subtract the first from the second argument and store the result in the third argument
• divi divide the first by the second argument and store the result in the third argument
• muli multiply the first by the second argument and store the result in the third argument
• shli shift left the first argument by the number of positions given by the second argument and store the result in the third argument
• shri shift right the first argument by the number of positions given by the second argument and store the result in the third argument
• seti set the first register argument to the second argument
• int calls the interrupt specified by the first (integer) argument

Control Flow

• jmp jump to the label given by the first argument
• lti execute next statement if argument 1 is less than argument 2 else skip the next statement
• gti execute next statement if argument 1 is greater than argument 2 else skip the next statement
• eqi execute the next statement if argument 1 is equal to argument 2 else skip the next statement

Interupts

• 0..9 range:
  • 0 put value of register A as ASCII character on stdout
  • 1 put value of register A as decimal integer on stdout