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54 mv_fox 1 
/*
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 * CD-ROM detection routines
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 * Copyright (C) 2016 Mateusz Viste
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 */
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#include <dos.h>
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#include "cdrom.h" /* include self for control */
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/* returns 1 if drive drv is a valid CDROM, zero if not, negative if no MSCDEX (0=A:, etc) */
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int cdrom_drivecheck(int drv) {
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  union REGS r;
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  r.x.ax = 0x150B;
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  r.x.cx = drv;
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  int86(0x2F, &r, &r);
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  if (r.x.bx != 0xADAD) return(-1); /* look for the MSCDEX signature */
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  if (r.x.ax == 0) return(0);
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  return(1);
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}
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/* returns the identifier of the first CDROM drive (0=A:, etc), or a negative value on error */
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int cdrom_findfirst(void) {
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  int i;
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  for (i = 2; i < 26; i++) { /* check drives from C to Z */
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    int cdres = cdrom_drivecheck(i);
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    if (cdres == 0) continue;
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    if (cdres == 1) return(i);
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    break;
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  }
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  return(-1);
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}