/*
Copyright (C) Magna Carta Software, Inc. 1990,1991.  All Rights Reserved.
C COMMUNICATIONS TOOLKIT
CPEEK.C -- Examine, but do not remove, bytes in the RX buffer.
*/


#include <cctdef.h>
#include <ccttype.h>


/*
C_RXPEEK -- examine, but do not remove, a byte in the receive buffer.
Parameters:
COMM_PORT *p -- pointer to the port;
WORD num     -- number of bytes from tail to read;
Return Value:
    the byte at the requested position;
    EOF if request fewer bytes in buffer than requested byte;
*/
short c_rxpeek(COMM_PORT *p, WORD num)
{
    short ret;
    unsigned oflow;

    if (p->rxbufhead > p->rxbuftail) {
        if (p->rxbuftail + num > p->rxbufhead) ret = -1;
        else ret = *(p->rxbuftail+num);
    }
    else {
        if (p->rxbuftail + num < p->rxbufend) ret = *(p->rxbuftail+num);
        else {
            oflow = num - (unsigned) (p->rxbufend - (BYTE FAR_ *) p->rxbuftail);
#if defined(VERSION70)
            if (p->rxbuf + oflow > p->rxbufhead) ret = -1;
#else
            if (oflow > (unsigned) (p->rxbufhead - p->rxbuf)) ret = -1;
#endif
            else ret = *(p->rxbuf+oflow);
        }
    }

    return (ret);
}