VMS Help MACRO, VAX MACRO Assembler, Instructions, SOBGxx  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Purpose:        Subtract one and branch - decrement integer loop count
                    and loop
    Format:         opcode index.ml,displ.bb
    Operation:      index = index - 1; if {{SOBGEQ} and {index GEQ 0}} or
                    {{SOBGTR} and {index GTR 0}} then
                    PC = PC + SEXT (displ)
    C. Codes:       N = {index LSS 0}, Z = {index EQL 0},
                    V = {integer overflow}, C = C
    Exceptions:     Integer overflow
    Opcodes:        F4    SOBGEQ   Subtract one, branch greater or equal
                    F5    SOBGTR   Subtract one, branch greater than