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Add reference tool

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Dale Weiler 2013-11-23 03:10:09 -05:00
parent 7011a2ef2c
commit 29f2cc302b
1 changed files with 38 additions and 0 deletions
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38
util.c
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@ -455,6 +455,44 @@ uint16_t util_crc16(uint16_t current, const char *k, size_t len) {
return h;
}
/*
* The table above can be created with the following utility. Which
* just builds the slices and the C array as well.
*/
#if 0
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
/* compile with cc -std=c99 */
int main(void) {
uint16_t tab[8][256];
for (unsigned i = 0; i < 0x100; ++i) {
uint16_t x = i << 8;
for (int j = 0; j < 8; ++j)
x = (x << 1) ^ ((x & 0x8000) ? 0x1021 : 0);
tab[0][i] = x;
}
for (unsigned i = 0; i < 0x100; ++i) {
uint16_t c = tab[0][i];
for (unsigned j = 1; j < 8; ++j) {
c = tab[0][c >> 8] ^ (c << 8);
tab[j][i] = c;
}
}
printf("static const uint16_t util_crc16_table[8][256] = {");
for (int i = 0; i < 8; ++i) {
printf("{\n");
for (int j = 0; j < 0x100; ++j) {
printf((j & 7) ? " " : " ");
printf((j != 0x100-1) ? "0x%04X," : "0x%04X", tab[i][j]);
if ((j & 7) == 7)
printf("\n");
}
printf((i != 7) ? "}," : "}");
}
printf("};\n");
}
#endif
/*
* modifier is the match to make and the transposition from it, while add is the upper-value that determines the