How would I push a negative number with OPCODES onto the stack?

Question

If the user wants to push -10 onto the stack.

Would I do "10 OP_NEGATE" ?

Or could I convert it to the hex value by doing 0x80 + 10 = 0X8A ?

Raghav Sood · Accepted Answer · 2018-05-06 09:18:30Z

1

Both will work. OP_NEGATE simply XORs with 0x80, so you can also directly push the result.

answered May 6, 2018 at 9:18

Raghav Sood

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And we take the absolute value of a signed integer right? In this case 10 could be written with one byte so I think that using two bytes was overkill?
– Kyle Graham
May 6, 2018 at 9:30
Not necessarily. Some operations, like hashing, will produce different results for positive or negative numbers. Some operations, like signatures, will fail if the R value is negative. It depends on what you're doing.
– Raghav Sood
May 6, 2018 at 14:08
1

Take into account that for numbers between -1 and 16 inclusive, short 1-byte opcodes exist. Pushing any other number (like -10) requires an explicit push operation of the bytes encoding of the number. Both "10 NEGATE" and "-10" are therefore 2-byte scripts.
– Pieter Wuille
May 6, 2018 at 23:45

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