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#include "util.h"
/* https://www.w3.org/TR/PNG/#D-CRCAppendix */
static uint32_t crc_table[256];
uint32_t crc32(const uint8_t *buf, size_t len) {
if (!crc_table[1]) {
for (int i = 0; i < 256; i++) {
uint32_t c = i;
for (int j = 0; j < 8; j++)
c = ((c&1) ? 0xedb88320 : 0) ^ (c >> 1);
crc_table[i] = c;
}
}
uint32_t c = 0xFFFFFFFF;
for (size_t i = 0; i < len; i++)
c = crc_table[(c ^ buf[i]) & 0xff] ^ (c >> 8);
return ~c;
}
uint16_t ip_checksum(const uint8_t *buf, size_t len) {
uint32_t c = 0;
while (len >= 2) {
c += nget16(buf);
buf += 2; len -= 2;
}
if (len) c += (*buf) << 8;
while (c >= 0xFFFF)
c = (c & 0xFFFF) + (c >> 16);
return ~c;
}
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