[WIP] script: prevent OP_NEGATE from generating negative zero. #18236

1. 
   v1048576 commented at 9:53 pm on March 1, 2020: none

   Prevent OP_NEGATE from generating negative zero since negative zero is implementation defined for C/C++.

   Do you agree with negative zero issue? Does this impact CastToBool since mentions negative zero? Looking for feedback as I am unsure how to test these changes?

2. Avoid negative zero?

   Prevent OP_NEGATE from generating negative zero.

   1ebc0f5c8b
3. v1048576 renamed this:
   script: prevent OP_NEGATE from generating negative zero.
   [WIP] script: prevent OP_NEGATE from generating negative zero.
   on Mar 1, 2020
4. 
   sipa commented at 10:00 pm on March 1, 2020: member

   This is a hardfork, and cannot be made unilaterally by one client - the entire network must choose this.

   It’s also misguided. Representation and existance of negative zero is indeed implementation defined for C++ int types, but also not observable and not what this is about. Bitcoin Script’s numeric interpration of byte vectors does have a well-defined and observable negative zero. We cannot get rid of it without enormous effort.

5. 
   v1048576 commented at 10:06 pm on March 1, 2020: none

   This is a hardfork, and cannot be made unilaterally by one client - the entire network must choose this.

   It’s also misguided. Representation and existance of negative zero is indeed implementation defined for C++ int types, but also not observable and not what this is about. Bitcoin Script’s numeric interpration of byte vectors does have a well-defined and observable negative zero. We cannot get rid of it without enormous effort.

   Thanks for the fast reply, definitely more complex than I realized. Can you recommend where to learn about Script negative zero behavior for byte vectors? Or do you have an example?

6. DrahtBot added the label Consensus on Mar 1, 2020
7. v1048576 closed this on Mar 1, 2020

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8. 
   sipa commented at 10:31 pm on March 1, 2020: member

   To be clear: it’s the CastToBool change that’s a hardfork. The script 0x0180 goes from being unspendable to spendable (it pushes a negative zero onto the stack). The change in OP_NEGATE is a no-op, as the arithmetic operations there operate on the converted-to-numbers representation, in which zero and negative zero are equal.
9. DrahtBot locked this on Feb 15, 2022

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