module Platform.AArch64.WordArithmetic

import Compiler.MachineAArch64
import Compiler.MachineAArch64Assembly
import Platform.AArch64.RoutineEmitter

-- x0 destination, x1 left, x2 right. Unsigned addition overflow is equivalent
-- to the wrapped sum being below the left operand. Test before storing so a
-- rejected update cannot change the destination or reuse a frame version.
-- Return zero on success or one on overflow, matching Runtime.NativeWordArithmetic.
def aarch64CheckedWordAddAssembly =
  (ahrEmit
    (constructor
      AArch64Instruction
      AArch64AddRegister
      (constructor AArch64Register AArch64X3)
      (constructor AArch64Register AArch64X1)
      (constructor AArch64Register AArch64X2))
    (ahrEmit
      (constructor
        AArch64Instruction
        AArch64CompareRegister
        (constructor AArch64Register AArch64X3)
        (constructor AArch64Register AArch64X1))
      (app
        (lambda unrestricted tail : (family AArch64Assembly) .
          (constructor
            AArch64Assembly
            AArch64AssemblyBranchIf
            (constructor AArch64Condition AArch64CarryClear)
            b"overflow"
            tail))
        (ahrEmit
          (constructor
            AArch64Instruction
            AArch64StoreMemory64
            (constructor AArch64Register AArch64X0)
            0
            (constructor AArch64Register AArch64X3))
          (ahrMovImm
            (constructor AArch64Register AArch64X0)
            0
            (ahrReturn
              (ahrLabel
                b"overflow"
                (ahrMovImm (constructor AArch64Register AArch64X0) 1 (ahrReturn ahrEnd)))))))))

def aarch64CheckedWordAddCode =
  (aarch64RoutineBytes aarch64CheckedWordAddAssembly)