AngoLinux |
80386 Programmer's Reference Manual -- Opcode BSR |
BSR -- Bit Scan Reverse
OperationIF r/m = 0 THEN ZF := 1; register := UNDEFINED; ELSE temp := OperandSize - 1; ZF := 0; WHILE BIT[r/m, temp] = 0 DO temp := temp - 1; register := temp; OD; FI; DescriptionBSR scans the bits in the second word or doubleword operand from the most significant bit to the least significant bit. The ZF flag is cleared if the bits are all 0; otherwise, ZF is set and the destination register is loaded with the bit index of the first set bit found when scanning in the reverse direction.Flags AffectedZF as described aboveProtected Mode Exceptions#GP(0) if the result is in a nonwritable segment; #GP(0) for an illegal memory operand effective address in the CS, DS, ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code) for a page faultReal Address Mode ExceptionsInterrupt 13 if any part of the operand would lie outside of the effective address space from 0 to 0FFFFHVirtual 8086 Mode ExceptionsSame exceptions as in Real Address Mode; #PF(fault-code) for a page fault
[Home Page dell'ITIS "Fermi"] [80386 Programmer's Reference Manual Index] [Previous] [Next] |