NASM 2.05 based x86 Instruction Reference[ch308]

A.5.284 SALC: Set AL from Carry Flag SALC ; D6 [8086,UNDOC] SALC is an early undocumented instruction similar in concept to SETcc (section A.5.287). Its function is to set AL to zero if the carry flag is clear, or to 0xFF if it is set.