Can there be concurrent updates? OI works fine if on any modern machine, given the interlocked access facilities.
If there are no worries about concurrent updates and you don't like executed instructions, Something like this (assumes AMODE 31, bit number < 4G): L area_address_reg,area_address L even_reg,bit_num SRDL even_reg,3 * even_reg has the byte offset SRL even_reg+1,29 * odd reg has which bit-within-byte IC some_reg,0(even_reg,area_address_reg) LHI OR_Reg,X'80' SRL OR_Reg,0(even_reg+1) OR some_reg,OR_reg STC some_reg,0(even_reg+1,address_reg) can be used. If there could be concurrent updates, the above approach will not work. Peter Relson z/OS Core Technology Design
