checksum.c

ADS下的bios工程

#include <bios/checksum.h>

unsigned int 
checksum(void *ptr, int len, unsigned int chksum)
{
    unsigned char    *p = (unsigned char *)ptr;
    int    i;

    for (i = 0; i < len - 1; i += 2)
        chksum += (p[i] << 8) | p[i + 1];

    if (len & 1)
        chksum += p[len - 1] << 8;

    chksum = (chksum & 0xffff) + (chksum >> 16);
    chksum = (chksum & 0xffff) + (chksum >> 16);

    return  chksum;
}