[En-Nut-Discussion] eboot, a tricky bit.

[Damian Slee]

I should have read on;
 
it looks like the ptr is being incremented
 
u_short *tmp;
tmp = (u_short *) data;
sum +=  *tmp;
data += sizeof(u_short);
 


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From: Damian Slee 
Sent: Friday, 20 February 2004 9:35 AM
To: Brett.Abbott at digital-telemetry.com; Ethernut User Chat (English)
Subject: RE: [En-Nut-Discussion] eboot, a tricky bit.


I'm pretty sure its incrementing the contents of memory, not the ptr.
the above/below code would help to double check.
u_short *tmp;
tmp = (u_short *) data;
*tmp++;  // or (*tmp)++   if it reads better
 

  _____  

From: Brett Abbott [mailto:Brett.Abbott at digital-telemetry.com] 
Sent: Friday, 20 February 2004 9:22 AM
To: en-nut-discussion at egnite.de
Subject: [En-Nut-Discussion] eboot, a tricky bit.


Hi

Ive almost completed the port to ICC of eboot but have found a segment
of code that has stumped my self taught C programming skills.  Could I
ask if someone could advise us of the appropriate ICC equivalent?

In particular, the line Im having trouble compiling is "sum +=
*((u_short *) data)++;"

Many Thanks, Any help appreciated.
Brett

from eboot\ip.c:

/*!
 * \brief Calculate the IP checksum over a block of data.
 *
 * \param data Pointer to the data block.
 * \param size Size of the data block.
 *
 * \return The checksum in network byte order.
 */
static u_short IpChkSum(const void *data, u_short size)
{
    register u_long sum = 0;

    for (;;) {
        if (size < 2)
            break;
        sum += *((u_short *) data)++;
        size -= 2;
    }
    if (size)
        sum += *(u_char *) data;

    while ((size = (u_short) (sum >> 16)) != 0)
        sum = (u_short) sum + size;

    return (u_short) sum ^ 0xFFFF;
}


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Email: Brett.Abbott at digital-telemetry.com
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