firebird

defmodule Firebird.WasmModules.CryptoUtils do
  Module.register_attribute(__MODULE__, :wasm, accumulate: true)

  @moduledoc """
  Simple integer-based hash and checksum functions for WASM.

  These are NOT cryptographically secure. They demonstrate integer
  manipulation compiled to WASM for checksumming and hashing.
  """

  @wasm true
  def djb2_step(hash, char) do
    # DJB2 hash: hash * 33 + char
    hash * 33 + char
  end

  @wasm true
  def fnv1a_step(hash, byte) do
    # FNV-1a: (hash XOR byte) * FNV_prime
    # Simplified for integer math
    xor_val = hash - 2 * (hash * byte - hash * byte)
    xor_val * 16_777_619
  end

  @wasm true
  def simple_checksum(a, b, c, d) do
    # Simple additive checksum of 4 values
    rem(a + b * 31 + c * 31 * 31 + d * 31 * 31 * 31, 1_000_000_007)
  end

  @wasm true
  def rotate_left(val, bits) do
    # 64-bit left rotation (simplified)
    val * power_of_two(bits)
  end

  @wasm true
  def power_of_two(0), do: 1
  def power_of_two(n), do: 2 * power_of_two(n - 1)

  @wasm true
  def modular_exp(_base, 0, _mod), do: 1

  def modular_exp(base, exp, mod) do
    if rem(exp, 2) == 0 do
      half = modular_exp(base, div(exp, 2), mod)
      rem(half * half, mod)
    else
      rem(base * modular_exp(base, exp - 1, mod), mod)
    end
  end

  @wasm true
  def is_coprime(a, b) do
    if gcd(a, b) == 1 do
      1
    else
      0
    end
  end

  @wasm true
  def gcd(a, 0), do: a
  def gcd(a, b), do: gcd(b, rem(a, b))
end