; 小貓中文 - XMS helpers, interrupt stubs and BIOS wrappers
; Copyright (C) 2026 HelloSun
; Author: HelloSun    First version: 1.0, 2026-10-25
; SPDX-License-Identifier: GPL-3.0-only
; Additional terms under GPLv3 section 7(b): the author attribution "HelloSun" and this copyright
; notice must be preserved in all copies and modified versions, including the notice the program
; displays when it starts. See LICENSE.
; See ../LICENSE for license terms.
;
; Watcom large model, register calling convention: args AX,DX,BX,CX; far return.
; Every helper preserves all registers except AX (return value).
; All variables live in the code segment so interrupt handlers never depend on DS.

bits 16
segment _TEXT public class=CODE

global xms_init_
global xms_query_
global xms_largest_
global xms_total_
global xms_alloc_
global xms_free_
global xms_move_
global install_hooks_
global save_vectors_
global set_handlers_
global is_installed_
global bios_peek_
global bios_getkey_
global bios10_call_
global get_rom_font_
global cpu_idle_

xms_entry:   dd 0
xms_freekb:  dw 0
xms_totalkb: dw 0
old16:       dd 0
old10:       dd 0
old2f:       dd 0
c_key:       dd 0
c_vid:       dd 0
s_ss:        dw 0
s_sp:        dw 0
busy16:      db 0
busy10:      db 0
res10:       dw 0

%macro SAVE 0
    push bx
    push cx
    push dx
    push si
    push di
    push bp
    push ds
    push es
%endmacro
%macro REST 0
    pop es
    pop ds
    pop bp
    pop di
    pop si
    pop dx
    pop cx
    pop bx
%endmacro

; ---------------------------------------------------------------- XMS
xms_init_:
    SAVE
    mov ax, 0x4310
    int 0x2F
    mov [cs:xms_entry], bx
    mov [cs:xms_entry+2], es
    REST
    mov ax, 1
    retf

xms_query_:
    SAVE
    mov ah, 0x08
    call far [cs:xms_entry]
    cld
    mov [cs:xms_freekb], ax
    mov [cs:xms_totalkb], dx
    REST
    retf

xms_largest_:
    mov ax, [cs:xms_freekb]
    retf

xms_total_:
    mov ax, [cs:xms_totalkb]
    retf

; unsigned xms_alloc(unsigned kb): returns handle or 0
xms_alloc_:
    SAVE
    mov dx, ax
    mov ah, 0x09
    call far [cs:xms_entry]
    cld
    cmp ax, 1
    jne .fail
    mov ax, dx
    jmp .out
.fail:
    xor ax, ax
.out:
    REST
    retf

xms_free_:
    SAVE
    mov dx, ax
    mov ah, 0x0A
    call far [cs:xms_entry]
    cld
    REST
    retf

; unsigned xms_move(unsigned seg, unsigned off): move-struct at seg:off
xms_move_:
    SAVE
    mov si, dx
    mov ds, ax
    mov ah, 0x0B
    call far [cs:xms_entry]
    cld
    REST
    retf

; ---------------------------------------------------------------- BIOS helpers
; unsigned bios_peek(void): key (AX) of pending key or 0 when none
bios_peek_:
    SAVE
    mov ah, 1
    pushf
    call far [cs:old16]
    jnz .have
    xor ax, ax
.have:
    REST
    retf

; unsigned bios_getkey(void): wait for key
bios_getkey_:
    SAVE
    xor ah, ah
    pushf
    call far [cs:old16]
    REST
    retf

; unsigned bios10_call(unsigned ax, unsigned bx): call previous INT 10h, returns AX
bios10_call_:
    push cx
    push dx
    push si
    push di
    push bp
    push ds
    push es
    mov bx, dx             ; second argument arrives in DX
    pushf
    call far [cs:old10]
    pop es
    pop ds
    pop bp
    pop di
    pop si
    pop dx
    pop cx
    retf

; void far *get_rom_font(void): ROM 8x16 font pointer (DX:AX), via INT 10h AX=1130h BH=6
get_rom_font_:
    push bx
    push cx
    push si
    push di
    push bp
    push ds
    push es
    mov ax, 0x1130
    mov bx, 0x0600
    int 0x10
    mov ax, bp
    mov dx, es
    pop es
    pop ds
    pop bp
    pop di
    pop si
    pop cx
    pop bx
    retf

; void cpu_idle(void): wait for next interrupt
cpu_idle_:
    sti
    hlt
    retf

; void set_handlers(key_off, key_seg, vid_off, vid_seg)
set_handlers_:
    mov [cs:c_key], ax
    mov [cs:c_key+2], dx
    mov [cs:c_vid], bx
    mov [cs:c_vid+2], cx
    retf

; unsigned is_installed(void)
is_installed_:
    SAVE
    mov ax, 0xD7A0
    int 0x2F
    cmp ax, 0x584D
    mov ax, 0
    jne .no
    mov ax, 1
.no:
    REST
    retf

; void save_vectors(void): remember the previous INT 10h/16h/2Fh handlers
save_vectors_:
    SAVE
    mov ax, 0x3516
    int 0x21
    mov [cs:old16], bx
    mov [cs:old16+2], es
    mov ax, 0x3510
    int 0x21
    mov [cs:old10], bx
    mov [cs:old10+2], es
    mov ax, 0x352F
    int 0x21
    mov [cs:old2f], bx
    mov [cs:old2f+2], es
    REST
    retf

; void install_hooks(void)
install_hooks_:
    SAVE
    push cs
    pop ds
    mov dx, int16_hook
    mov ax, 0x2516
    int 0x21
    mov dx, int10_hook
    mov ax, 0x2510
    int 0x21
    mov dx, int2f_hook
    mov ax, 0x252F
    int 0x21
    REST
    retf

; ---------------------------------------------------------------- INT 2Fh
int2f_hook:
    cmp ax, 0xD7A0
    jne .chain
    mov ax, 0x584D
    iret
.chain:
    jmp far [cs:old2f]

; ---------------------------------------------------------------- INT 16h
int16_hook:
    cmp ah, 0
    je .mine
    cmp ah, 1
    je .mine
    cmp ah, 0x10
    je .mine
    cmp ah, 0x11
    je .mine
.chain:
    jmp far [cs:old16]
.mine:
    cmp byte [cs:busy16], 0
    jne .chain
    mov byte [cs:busy16], 1
    SAVE
    mov [cs:s_ss], ss
    mov [cs:s_sp], sp
    mov bx, cs
    cli
    mov ss, bx
    mov sp, stack_top
    sti
    cld
    call far [cs:c_key]
    cli
    mov ss, [cs:s_ss]
    mov sp, [cs:s_sp]
    sti
    REST
    mov byte [cs:busy16], 0
    or ax, ax
    retf 2

; ---------------------------------------------------------------- INT 10h
; The C handler receives a far pointer to the saved register frame
; (es ds bp di si dx cx bx ax ip cs flags) and returns 0 = handled, 1 = chain.
int10_hook:
    cmp byte [cs:busy10], 0
    jne .chain
    mov byte [cs:busy10], 1
    push ax
    push bx
    push cx
    push dx
    push si
    push di
    push bp
    push ds
    push es
    mov [cs:s_ss], ss
    mov [cs:s_sp], sp
    mov ax, cs
    cli
    mov ss, ax
    mov sp, stack_top
    sti
    cld
    mov ax, [cs:s_sp]
    mov dx, [cs:s_ss]
    call far [cs:c_vid]
    mov [cs:res10], ax
    cli
    mov ss, [cs:s_ss]
    mov sp, [cs:s_sp]
    sti
    pop es
    pop ds
    pop bp
    pop di
    pop si
    pop dx
    pop cx
    pop bx
    pop ax
    mov byte [cs:busy10], 0
    cmp word [cs:res10], 0
    jne .chain
    iret
.chain:
    jmp far [cs:old10]

; private stack for interrupt work
stack:
    times 2048 db 0
stack_top: