62 lines
1.1 KiB
C
62 lines
1.1 KiB
C
/* oneC_sum() - One complement's checksum Author: Kees J. Bot
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* 8 May 1995
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* See RFC 1071, "Computing the Internet checksum"
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*/
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#include <sys/types.h>
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#include <net/gen/oneCsum.h>
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u16_t oneC_sum(u16_t prev, void *data, size_t size)
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{
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u8_t *dptr;
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size_t n;
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u16_t word;
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u32_t sum;
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int swap= 0;
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sum= prev;
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dptr= data;
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n= size;
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swap= ((size_t) dptr & 1);
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if (swap) {
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sum= ((sum & 0xFF) << 8) | ((sum & 0xFF00) >> 8);
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if (n > 0) {
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((u8_t *) &word)[0]= 0;
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((u8_t *) &word)[1]= dptr[0];
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sum+= (u32_t) word;
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dptr+= 1;
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n-= 1;
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}
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}
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while (n >= 8) {
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sum+= (u32_t) ((u16_t *) dptr)[0]
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+ (u32_t) ((u16_t *) dptr)[1]
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+ (u32_t) ((u16_t *) dptr)[2]
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+ (u32_t) ((u16_t *) dptr)[3];
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dptr+= 8;
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n-= 8;
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}
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while (n >= 2) {
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sum+= (u32_t) ((u16_t *) dptr)[0];
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dptr+= 2;
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n-= 2;
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}
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if (n > 0) {
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((u8_t *) &word)[0]= dptr[0];
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((u8_t *) &word)[1]= 0;
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sum+= (u32_t) word;
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}
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sum= (sum & 0xFFFF) + (sum >> 16);
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if (sum > 0xFFFF) sum++;
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if (swap) {
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sum= ((sum & 0xFF) << 8) | ((sum & 0xFF00) >> 8);
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}
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return sum;
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}
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