WebAssembly Conditionals

Key Concepts of Conditionals in WebAssembly

1. Conditional Logic: WebAssembly supports conditional execution using the if instruction. The else instruction is optional and provides an alternative code path.
2. Structured Format: WebAssembly uses structured blocks for conditionals, defined by labels, making the code easy to parse and verify.
3. Boolean Evaluation: Conditions in WebAssembly are represented as integers:
   • A non-zero value is considered true.
   • Zero is considered false.
4. Syntax: Conditional blocks in WebAssembly are explicitly defined using if,else and end instructions.

Syntax of WebAssembly Conditionals

Here is a basic syntax example for a conditional block in WebAssembly:

(if (condition)
  (then
    ;; Code to execute if condition is true
  )
  (else
    ;; Code to execute if condition is false
  )
)

• if: Evaluates the condition. If true, executes the then block.
• else: Executes if the condition is false. This is optional.
• end: Marks the end of the conditional block.

Example 1: Basic Conditional Statement

This example demonstrates a simple conditional in WebAssembly that checks whether a number is positive.

(module
  (func $check_positive (param $num i32) (result i32)
    local.get $num            ;; Load the parameter
    i32.const 0               ;; Push 0 to the stack
    i32.gt_s                  ;; Compare: $num > 0
    if (result i32)           ;; If true, execute the then block
      i32.const 1             ;; Return 1 (positive)
    else
      i32.const 0             ;; Return 0 (not positive)
    end
  )
)

Explanation:

• Condition: i32.gt_s checks if $num is greater than 0.
• Result: Returns 1 if true, otherwise 0.

Example 2: Nested Conditionals

You can nest conditionals to handle multiple conditions.

(module
  (func $number_check (param $num i32) (result i32)
    local.get $num
    i32.const 0
    i32.eq
    if (result i32)          ;; Check if the number is zero
      i32.const 0            ;; Return 0 for zero
    else
      local.get $num
      i32.const 0
      i32.gt_s
      if (result i32)        ;; Check if the number is positive
        i32.const 1          ;; Return 1 for positive
      else
        i32.const -1         ;; Return -1 for negative
      end
    end
  )
)

Explanation:

• Checks if the number is zero, positive, or negative.
• Uses nested if-else blocks for clarity and precision.

Real-World Applications of Conditionals in WebAssembly

1. Dynamic Web Applications:
   • Adjust application behavior based on user input.
2. Data Validation:
   • Verify conditions such as value ranges or states before proceeding.
3. Game Logic:
   • Handle decision-making processes like player actions or AI behavior.

Debugging Conditionals in WebAssembly

1. Logging Results: Use JavaScript integration to export intermediate values for debugging.
2. Browser DevTools: Tools like Chrome’s WebAssembly debugger can visualize execution flow.
3. Testing Edge Cases: Ensure all possible paths in your conditional logic are tested.

Advanced Concepts: Multi-Condition Evaluation

WebAssembly conditionals can become complex when evaluating multiple conditions. Combining operators like and (&&) and or (| |) can simplify such scenarios.

Example: Multiple Conditions

(module
  (func $check_range (param $num i32) (result i32)
    local.get $num
    i32.const 10
    i32.ge_s
    local.get $num
    i32.const 20
    i32.le_s
    i32.and                  ;; Check if 10 <= num <= 20
    if (result i32)
      i32.const 1            ;; Return 1 if true
    else
      i32.const 0            ;; Return 0 if false
    end
  )
)