3 ms·

I know the docs say it has to be a bunch of zeroes at the start, the actual test is whether or not the generated value is below a certain number.

ars_technician 13y ago
When you are looking at a binary number, the number of zeros at the start is the exact same thing as making sure the number is below a certain threshold.
- lololomg 13y ago
  No it's not the exact same thing. Example: Treshold = 001010 If you check 001011 or 001001 then the number of leading zeros are the same but one number is below the threshold and the other is not.
- letstryagain 13y ago
  Not exactly the same thing. Consider this example: Threshold is 001010 The numbers 001001 and 001011 have the same number of leading zeroes but one is below the threshold and the other is not.
  - ars_technician 13y ago
    What I said is correct, but I suppose ambiguous. What I mean to say is that counting MSB zeros does specify that the number will be below a threshold, just not an arbitrary threshold like the one you gave in your example. For a more concrete example, if the requirement is that a 16-bit word is less than 4096, you only have to verify that it leads with 4 zeros.
    - letstryagain 13y ago
      Yes but Bitcoin uses 'below number X' which has more precision than just counting leading zeroes.
nilkn 13y ago
So the procedure described by blibble isn't actually used in the client software? I've always thought that's how it worked since that is what is written in the original Bitcoin paper (which has for a long time been my only source of information on the protocol).
- maaku 13y ago
  Yes blibble's procedure has nothing to do with the actual calculation. The protocol says to treat the 256-bit hash as a little-endian integer, and then check if that is less than the target value. The target value is an integer value that is stored as a custom-format floating point value in the block header and adjusted every 2016 blocks. "Difficulty" per se doesn't actually exist at the protocol level, it's a purely human-interface concern.

ars_technician 13y ago

When you are looking at a binary number, the number of zeros at the start is the exact same thing as making sure the number is below a certain threshold.

lololomg 13y ago
No it's not the exact same thing. Example: Treshold = 001010 If you check 001011 or 001001 then the number of leading zeros are the same but one number is below the threshold and the other is not.
letstryagain 13y ago
Not exactly the same thing. Consider this example: Threshold is 001010 The numbers 001001 and 001011 have the same number of leading zeroes but one is below the threshold and the other is not.
- ars_technician 13y ago
  What I said is correct, but I suppose ambiguous. What I mean to say is that counting MSB zeros does specify that the number will be below a threshold, just not an arbitrary threshold like the one you gave in your example. For a more concrete example, if the requirement is that a 16-bit word is less than 4096, you only have to verify that it leads with 4 zeros.
  - letstryagain 13y ago
    Yes but Bitcoin uses 'below number X' which has more precision than just counting leading zeroes.

nilkn 13y ago

So the procedure described by blibble isn't actually used in the client software? I've always thought that's how it worked since that is what is written in the original Bitcoin paper (which has for a long time been my only source of information on the protocol).

maaku 13y ago
Yes blibble's procedure has nothing to do with the actual calculation. The protocol says to treat the 256-bit hash as a little-endian integer, and then check if that is less than the target value. The target value is an integer value that is stored as a custom-format floating point value in the block header and adjusted every 2016 blocks. "Difficulty" per se doesn't actually exist at the protocol level, it's a purely human-interface concern.