example was incorrect

the example event id had 21 leading zeroes, not 20

I provided new C code that has been tested to work (I couldn't get the original example code to work) and I provided some JavaScript code to test event ids as well.

I did not re-compute the event id for the example event; I simply changed the nonce to be 21. Since it is an example, it may not matter that the event id is not correct.
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@ -10,6 +10,8 @@ This NIP defines a way to generate and interpret Proof of Work for nostr notes.
`difficulty` is defined to be the number of leading zero bits in the `NIP-01` id. For example, an id of `000000000e9d97a1ab09fc381030b346cdd7a142ad57e6df0b46dc9bef6c7e2d` has a difficulty of `36` with `36` leading 0 bits.
`002f...` is `0000 0000 0010 1111...` in binary, which has 10 leading zeroes. Do not forget to count leading zeroes for hex digits <= `7`.
Mining
------
@ -36,7 +38,7 @@ Example mined note
[
"nonce",
"776797",
"20"
"21"
]
],
"content": "It's just me mining my own business",
@ -47,33 +49,61 @@ Example mined note
Validating
----------
Here is some reference C code for calculating the difficulty (aka number of leading zero bits) in a nostr note id:
Here is some reference C code for calculating the difficulty (aka number of leading zero bits) in a nostr event id:
```c
int zero_bits(unsigned char b)
{
int n = 0;
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
if (b == 0)
return 8;
int countLeadingZeroes(const char *hex) {
int count = 0;
while (b >>= 1)
n++;
for (int i = 0; i < strlen(hex); i++) {
int nibble = (int)strtol((char[]){hex[i], '\0'}, NULL, 16);
if (nibble == 0) {
count += 4;
} else {
count += __builtin_clz(nibble) - 28;
break;
}
}
return 7-n;
return count;
}
/* find the number of leading zero bits in a hash */
int count_leading_zero_bits(unsigned char *hash)
{
int bits, total, i;
for (i = 0, total = 0; i < 32; i++) {
bits = zero_bits(hash[i]);
total += bits;
if (bits != 8)
break;
}
return total;
int main(int argc, char *argv[]) {
if (argc != 2) {
fprintf(stderr, "Usage: %s <hex_string>\n", argv[0]);
return 1;
}
const char *hex_string = argv[1];
int result = countLeadingZeroes(hex_string);
printf("Leading zeroes in hex string %s: %d\n", hex_string, result);
return 0;
}
```
Here is some JavaScript code for doing the same thing:
```javascript
// hex should be a hexadecimal string (with no 0x prefix)
function countLeadingZeroes(hex) {
let count = 0;
for (let i = 0; i < hex.length; i++) {
const nibble = parseInt(hex[i], 16);
if (nibble === 0) {
count += 4;
} else {
count += Math.clz32(nibble) - 28;
break;
}
}
return count;
}
```