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404 mateuszvis 1 
/*
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 * cls
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 */
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static int cmd_cls(struct cmd_funcparam *p) {
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  unsigned char screenw, screenh;
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  const char *ansiesc = "\x1B[2J$";
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  if (cmd_ishlp(p)) {
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    outputnl("Clears the screen");
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    outputnl("");
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    outputnl("CLS");
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    return(-1);
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  }
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  screenw = screen_getwidth();
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  screenh = screen_getheight();
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  _asm {
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    /* output an ANSI ESC code for "clear screen" in case the console is
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     * some kind of terminal */
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    mov ah, 0x09     /* write $-terminated string to stdout */
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    mov dx, ansiesc
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    int 0x21
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    /* check what stdout is set to */
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    mov ax, 0x4400   /* IOCTL query device/flags flags */
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    mov bx, 1        /* file handle (1 = stdout) */
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    int 0x21         /* CF set on error, otherwise DX set with flags */
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    jc DONE          /* abort on error */
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    /* DX = 10000010
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            |   |||
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            |   ||+--- indicates standard output
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            |   |+---- set if NUL device
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            |   +----- set if CLOCK device
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            +--------- set if handle is a device (ie. not a file)
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            in other words, DL & 10001110 (8Eh) should result in 10000010 (82h)
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            */
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    and dl, 0x8e
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    cmp dl, 0x82
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    jne DONE         /* abort on error */
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    /* scroll vram out of screen */
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    mov ax, 0x0600   /* scroll up entire rectangle */
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    mov bh, 0x07     /* fill screen with white-on-black */
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    xor cx, cx       /* upper left location in CH,CL (0,0) */
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    /* DX is bottom right location of rectangle (DH=row, DL=column) */
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    mov dh, [screenh]
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    dec dh
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    mov dl, [screenw]
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    dec dl
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    int 0x10
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    /* set cursor to top left corner (0,0) of the screen */
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    mov ah, 0x02     /* set cursor position */
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    xor bh, bh       /* page number */
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    xor dx, dx       /* location in DH,DL */
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    int 0x10
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    DONE:
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  }
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  return(-1);
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}