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_dos_setblock
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─────Run-Time Library───────────────────────────────────────────────────────
 
     The _dos_setblock routine uses system call 0x4A to change the
     size of <seg>, previously allocated by _dos_allocmem, to <size>
     paragraphs. If the request cannot be satisfied, the maximum
     possible segment size is copied to the buffer pointed to by
     <maxsize>.
 
     Return Value
 
     The function returns 0 if successful. If the call fails, it
     returns the DOS error code and sets errno to ENOMEM, indicating
     that a bad segment value was passed (one that does not correspond
     to a segment returned from a previous _dos_allocmem call) or one
     that contains invalid arena headers.
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