What restrictions does the model discipline within the block header have?

nVersion is a 4-byte little-endian signed integer. Little-endianness signifies that the least vital byte is first. The order of bits in a byte stays the identical.

I’m conscious of the next restrictions:

• BIP65 requires blocks to have a minimum of model 4.
• Since nVersion is a signed integer, setting the highest bit would flip it unfavorable.

Due to this fact, any bit sample that doesn’t set the highest bit and units a minimum of one bit amongst positions 2…30 shall be permitted.

Be aware that within the context of BIP-9-style deployments, the highest three bits have to be set to 001 and solely in that case the remaining bits are interpreted as a bit vector the place every place might sign readiness for a softfork proposal’s activation.

Let’s take a look at some examples in hexadecimal and binary:

Signal (topbit):

0b 00000000 00000000 00000000 ±0000000
                              ^
                              Signal (topbit)

Model 0, least and most important bytes:

0x 00       00       00       00
0b 00000000 00000000 00000000 00000000
   ^______^                   ^______^
     LSB                        MSB

Model 1:

0x 01       00       00       00
0b 00000001 00000000 00000000 00000000

Model 4:

0x 04       00       00       00
0b 00000100 00000000 00000000 00000000

BIP-9 (not signaling):

0x 00       00       00       20
0b 00000000 00000000 00000000 00100000

Signaling for Taproot on bit 2:

0x 04       00       00       20
0b 00000100 00000000 00000000 00100000

Model of Block 779,960 (instance for Overt ASICBOOST):

0x 32       47       40       00
0b 00110010 01000111 01000000 00000000