What does 0 and U mean on the flags?

Wondering what 0 and U mean on the metadata for the flags, as in:

OF=U SF=U ZF=U AF=U PF=U CF=U
OF=0 SF=W ZF=W AF=U PF=W CF=0

Also what do the lowercase x vs. uppercase X mean, and lowercase w and W?

x:~r8/m8,~r8

[kobalicek]

• ib - signed byte
• ub - unsigned byte
• iw - signed word
• uw - unsigned word
• id - signed doubleword
• ud - unsigned doubleword
• iq - signed quadword
• uq - unsigned quadword

AsmDB provides some extensions that are either not part of the opcode in the manual or that are written in the docs somewhere. For example imagine add r32, immediate - you have multiple options: add r32, ib - immediate encoded as byte, or add r32, id/ud - immediate encoded as dword - doesn’t matter whether it’s signed or unsigned.

AsmJit then is able to validate the instruction, so add r32, -1 would be the same as add r32, 0xFFFFFFFF - but add r64, -1 is not the same as add r64, 0xFFFFFFFF.

[kobalicek]

• 0 - set to zero
• 1 - set to one
• U - undefined (according to the instruction manual)
• ~ - commutative (swapping operands won’t change the result)
• x - partial read/write (8-bit and 16-bit GP ops mostly)
• X - full read/write (with possible zero extension)
• w - partial write (8-bit and 16-bit GP ops mostly)
• W - full write (with possible zero extension)