Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

parity flag

An x86 flag that ucomisd sets to 1 when a comparison involved a NaN, which compiled code checks with jp.

PF (bit 2 of RFLAGS) originally records the even parity of a result's low byte; after ucomisd/ucomiss it is 1 exactly when the comparison is unordered, so == and != on doubles test it with jp/jnp or setnp.

See also

floating-point compare unordered comparison NaN status flags

Read the full section →

snap pen only