__cdecl16near Calling Convention
Purpose: Used for calling near (within the same segment) functions in 16-bit code.
Stack Management: The caller cleans up the stack after the function call.
Parameter Passing: Parameters are pushed onto the stack from right to left.
Return Address: A near return address (16-bit) is pushed onto the stack.
Return Value: The return value is typically placed in the AX register.

e.g

; Caller
push param2
push param1
call near_func
add sp, 4  ; Clean up the stack (2 parameters * 2 bytes each)

; Callee (near_func)
near_func:
  push bp
  mov bp, sp
  ; Function body
  mov sp, bp
  pop bp
  ret

__cdecl16far Calling Convention
Purpose: Used for calling far (across different segments) functions in 16-bit code.
Stack Management: The caller cleans up the stack after the function call.
Parameter Passing: Parameters are pushed onto the stack from right to left.
Return Address: A far return address (32-bit, consisting of a segment and an offset) is pushed onto the stack.
Return Value: The return value is typically placed in the AX register.

e.g

; Caller
push param2
push param1
call far_func
add sp, 4  ; Clean up the stack (2 parameters * 2 bytes each)

; Callee (far_func)
far_func:
  push bp
  mov bp, sp
  ; Function body
  mov sp, bp
  pop bp
  retf  ; Far return

Key Differences
Return Address: __cdecl16near uses a 16-bit return address, while __cdecl16far uses a 32-bit return address (segment:offset).
Function Scope: __cdecl16near is for functions within the same segment, whereas __cdecl16far is for functions that may be in different segments.
Return Instruction: __cdecl16near uses ret, while __cdecl16far uses retf (far return).


### REGISTERS ###

Register Usage in __cdecl16near and __cdecl16far
Caller-Saved Registers (Volatile)
These registers must be saved by the caller if they wish to preserve their values across function calls:

AX: Accumulator register, often used for return values.
CX: Counter register, commonly used in loops and string operations.
DX: Data register, used for I/O operations and arithmetic.
SI: Source index for string operations.
DI: Destination index for string operations.
Callee-Saved Registers (Non-Volatile)
These registers must be preserved by the callee. If the callee uses these registers, it must save their original values and restore them before returning:

BP: Base pointer, used for stack frame management.
SP: Stack pointer, although typically managed by the calling convention itself.
BX: Base register, often used for addressing.
SI: Source index, if not used for string operations.
DI: Destination index, if not used for string operations.

e.g

; Caller
push param2
push param1
call near_func
add sp, 4  ; Clean up the stack (2 parameters * 2 bytes each)

; Callee (near_func)
near_func:
  push bp
  mov bp, sp
  ; Save callee-saved registers if used
  push bx
  push si
  push di
  ; Function body
  ; Use AX, CX, DX freely
  mov ax, [bp+4]  ; Access first parameter
  mov bx, [bp+6]  ; Access second parameter
  ;
  ; your other code here
  ;
  ; Restore callee-saved registers
  pop di
  pop si
  pop bx
  mov sp, bp
  pop bp
  ret