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Title: Difficulty with Difficulty Post by: haylingwriters on May 30, 2018, 08:44:40 AM I am using Bitcoin Core 64-bit, 0.16.0 (on Windows 7) and I am playing around with PHP to access Bitcoin client with RPC.
It's all going quite well but I have hit a bit of a roadblock trying to process Difficulty. The "GetDifficulty" RPC call returns a value like 4306949573981.513 How do I transform this value into an actual target like 0x1b0404cb ? Title: Re: Difficulty with Difficulty Post by: bob123 on May 30, 2018, 09:02:52 AM ~~Edit: Statement corrected, calculation in second post~~
For example: If the packed target from the block is 0x1b0404cb, the target you are looking for is: Code: 0x0404cb * 2**(8*(0x1b - 3)) = 0x00000000000404CB000000000000000000000000000000000000000000000000 Source: https://en.bitcoin.it/wiki/Difficulty#How_is_difficulty_stored_in_blocks.3F (https://en.bitcoin.it/wiki/Difficulty#How_is_difficulty_stored_in_blocks.3F) Title: Re: Difficulty with Difficulty Post by: haylingwriters on May 30, 2018, 09:27:36 AM First, you need to convert your decimal number into hex. Then you will have a packed represantation of the target. Thanks for the quick reply. A problem I have is how to interpret the number returned, for example 4306949573981.513 What does the period represent? Is it simply a decimal point? If so, do I ignore the digits to the right of the decimal point when converting the number to hex? Does the period represent a floating point number? Title: Re: Difficulty with Difficulty Post by: bob123 on May 30, 2018, 12:06:25 PM First, you need to convert your decimal number into hex. Then you will have a packed represantation of the target. Thanks for the quick reply. A problem I have is how to interpret the number returned, for example 4306949573981.513 What does the period represent? Is it simply a decimal point? If so, do I ignore the digits to the right of the decimal point when converting the number to hex? Does the period represent a floating point number? I have to correct my statement, please ignore those two sentences. getDifficulty() returns the factor (decimal) which describes how much more difficult it is to find a block, relative to the difficulty at the highest possible target (highest target = lowest difficulty). Difficulty = largest possible target / current target. So to calculate the target you have to divide the largest possible target (0x00000000FFFF0000000000000000000000000000000000000000000000000000) by the difficulty. In your case: Largest possible target: (0x00000000FFFF0000000000000000000000000000000000000000000000000000)16 = (26959535291011309493156476344723991336010898738574164086137773096960)10 Largest target / difficulty: 26959535291011309493156476344723991336010898738574164086137773096960) / 4306949573981.513 = 6.2595428 * 1054 Converted into hex: 0x415A48FC207EB1A005D72938CFF3FCCF0A000000000000 Now padding with leading 0's until length = 64: 0x000000000000000000415A48FC207EB1A005D72938CFF3FCCF0A000000000000 So the current target is : 000000000000000000415A48FC207EB1A005D72938CFF3FCCF0A000000000000 The hash of the latest block (https://blockchain.info/de/block/0000000000000000003424388ace9f93daaaf2980e41fcf0408e0c6f10800de9) is 0000000000000000003424388ace9f93daaaf2980e41fcf0408e0c6f10800de9 Title: Re: Difficulty with Difficulty Post by: haylingwriters on May 30, 2018, 02:49:50 PM Excellent response. Thank you. I found that the digits to the right of the decimal point in the value returned from Getdifficulty can safely be ignored.
Now, once I have figured how to handle the very large numbers in PHP I should be in good shape. Title: Re: Difficulty with Difficulty Post by: LoyceV on May 30, 2018, 07:17:52 PM Now, once I have figured how to handle the very large numbers in PHP I should be in good shape. Can you use bc (https://linux.die.net/man/1/bc) (see PHP: BC Math (http://php.net/manual/en/book.bc.php)?Code: echo 26959535291011309493156476344723991336010898738574164086137773096960 / 4306949573981.513 | bc Title: Re: Difficulty with Difficulty Post by: haylingwriters on May 31, 2018, 01:20:07 PM Now, once I have figured how to handle the very large numbers in PHP I should be in good shape. Can you use bc (https://linux.die.net/man/1/bc) (see PHP: BC Math (http://php.net/manual/en/book.bc.php)?Code: echo 26959535291011309493156476344723991336010898738574164086137773096960 / 4306949573981.513 | bc The actual arithmetic (floating point) was not too much of a problem, the challenge was converting the result to hex. I managed to find a bit of code on the web which did the job a treat. https://stackoverflow.com/questions/5301034/how-to-generate-random-64-bit-value-as-decimal-string-in-php/5302533#5302533 (https://stackoverflow.com/questions/5301034/how-to-generate-random-64-bit-value-as-decimal-string-in-php/5302533#5302533) (Section 2 of the above link.) |