diff options
Diffstat (limited to 'lib/checksum.c')
| -rw-r--r-- | lib/checksum.c | 148 |
1 files changed, 73 insertions, 75 deletions
diff --git a/lib/checksum.c b/lib/checksum.c index 3d6cd45791..8eef73e243 100644 --- a/lib/checksum.c +++ b/lib/checksum.c @@ -9,13 +9,13 @@ #include <zebra.h> #include "checksum.h" -int /* return checksum in low-order 16 bits */ -in_cksum(void *parg, int nbytes) +int /* return checksum in low-order 16 bits */ + in_cksum(void *parg, int nbytes) { u_short *ptr = parg; - register long sum; /* assumes long == 32 bits */ - u_short oddbyte; - register u_short answer; /* assumes u_short == 16 bits */ + register long sum; /* assumes long == 32 bits */ + u_short oddbyte; + register u_short answer; /* assumes u_short == 16 bits */ /* * Our algorithm is simple, using a 32-bit accumulator (sum), @@ -24,15 +24,15 @@ in_cksum(void *parg, int nbytes) */ sum = 0; - while (nbytes > 1) { + while (nbytes > 1) { sum += *ptr++; nbytes -= 2; } - /* mop up an odd byte, if necessary */ + /* mop up an odd byte, if necessary */ if (nbytes == 1) { - oddbyte = 0; /* make sure top half is zero */ - *((u_char *) &oddbyte) = *(u_char *)ptr; /* one byte only */ + oddbyte = 0; /* make sure top half is zero */ + *((u_char *)&oddbyte) = *(u_char *)ptr; /* one byte only */ sum += oddbyte; } @@ -40,82 +40,80 @@ in_cksum(void *parg, int nbytes) * Add back carry outs from top 16 bits to low 16 bits. */ - sum = (sum >> 16) + (sum & 0xffff); /* add high-16 to low-16 */ - sum += (sum >> 16); /* add carry */ - answer = ~sum; /* ones-complement, then truncate to 16 bits */ - return(answer); + sum = (sum >> 16) + (sum & 0xffff); /* add high-16 to low-16 */ + sum += (sum >> 16); /* add carry */ + answer = ~sum; /* ones-complement, then truncate to 16 bits */ + return (answer); } /* Fletcher Checksum -- Refer to RFC1008. */ #define MODX 4102U /* 5802 should be fine */ -/* To be consistent, offset is 0-based index, rather than the 1-based +/* To be consistent, offset is 0-based index, rather than the 1-based index required in the specification ISO 8473, Annex C.1 */ /* calling with offset == FLETCHER_CHECKSUM_VALIDATE will validate the checksum without modifying the buffer; a valid checksum returns 0 */ -u_int16_t -fletcher_checksum(u_char * buffer, const size_t len, const uint16_t offset) +u_int16_t fletcher_checksum(u_char *buffer, const size_t len, + const uint16_t offset) { - u_int8_t *p; - int x, y, c0, c1; - u_int16_t checksum = 0; - u_int16_t *csum; - size_t partial_len, i, left = len; - - if (offset != FLETCHER_CHECKSUM_VALIDATE) - /* Zero the csum in the packet. */ - { - assert (offset < (len - 1)); /* account for two bytes of checksum */ - csum = (u_int16_t *) (buffer + offset); - *(csum) = 0; - } - - p = buffer; - c0 = 0; - c1 = 0; - - while (left != 0) - { - partial_len = MIN(left, MODX); - - for (i = 0; i < partial_len; i++) + u_int8_t *p; + int x, y, c0, c1; + u_int16_t checksum = 0; + u_int16_t *csum; + size_t partial_len, i, left = len; + + if (offset != FLETCHER_CHECKSUM_VALIDATE) + /* Zero the csum in the packet. */ { - c0 = c0 + *(p++); - c1 += c0; + assert(offset + < (len - 1)); /* account for two bytes of checksum */ + csum = (u_int16_t *)(buffer + offset); + *(csum) = 0; } - c0 = c0 % 255; - c1 = c1 % 255; - - left -= partial_len; - } - - /* The cast is important, to ensure the mod is taken as a signed value. */ - x = (int)((len - offset - 1) * c0 - c1) % 255; - - if (x <= 0) - x += 255; - y = 510 - c0 - x; - if (y > 255) - y -= 255; - - if (offset == FLETCHER_CHECKSUM_VALIDATE) - { - checksum = (c1 << 8) + c0; - } - else - { - /* - * Now we write this to the packet. - * We could skip this step too, since the checksum returned would - * be stored into the checksum field by the caller. - */ - buffer[offset] = x; - buffer[offset + 1] = y; - - /* Take care of the endian issue */ - checksum = htons((x << 8) | (y & 0xFF)); - } - - return checksum; + p = buffer; + c0 = 0; + c1 = 0; + + while (left != 0) { + partial_len = MIN(left, MODX); + + for (i = 0; i < partial_len; i++) { + c0 = c0 + *(p++); + c1 += c0; + } + + c0 = c0 % 255; + c1 = c1 % 255; + + left -= partial_len; + } + + /* The cast is important, to ensure the mod is taken as a signed value. + */ + x = (int)((len - offset - 1) * c0 - c1) % 255; + + if (x <= 0) + x += 255; + y = 510 - c0 - x; + if (y > 255) + y -= 255; + + if (offset == FLETCHER_CHECKSUM_VALIDATE) { + checksum = (c1 << 8) + c0; + } else { + /* + * Now we write this to the packet. + * We could skip this step too, since the checksum returned + * would + * be stored into the checksum field by the caller. + */ + buffer[offset] = x; + buffer[offset + 1] = y; + + /* Take care of the endian issue */ + checksum = htons((x << 8) | (y & 0xFF)); + } + + return checksum; } |