image/svg+xmlPOPCNT — Return the Count of Number of Bits Set to 1Instruction Operand EncodingDescriptionThis instruction calculates the number of bits set to 1 in the second operand (source) and returns the count in the first operand (a destination register).OperationCount = 0;For (i=0; i < OperandSize; i++) { IF (SRC[ i] = 1) // i’th bitTHEN Count++; FI;}DEST := Count;Flags AffectedOF, SF, ZF, AF, CF, PF are all cleared. ZF is set if SRC = 0, otherwise ZF is cleared.Intel C/C++ Compiler Intrinsic EquivalentPOPCNT: int _mm_popcnt_u32(unsigned int a);POPCNT: int64_t _mm_popcnt_u64(unsigned __int64 a);Protected Mode Exceptions#GP(0)If a memory operand effective address is outside the CS, DS, ES, FS or GS segments.#SS(0)If a memory operand effective address is outside the SS segment limit.#PF (fault-code)For a page fault.#AC(0)If an unaligned memory reference is made while the current privilege level is 3 and alignment checking is enabled.#UDIf CPUID.01H:ECX.POPCNT [Bit 23] = 0.If LOCK prefix is used.Real-Address Mode Exceptions#GP(0)If any part of the operand lies outside of the effective address space from 0 to 0FFFFH.#SS(0)If a memory operand effective address is outside the SS segment limit.#UDIf CPUID.01H:ECX.POPCNT [Bit 23] = 0.If LOCK prefix is used.OpcodeInstructionOp/ En64-Bit ModeCompat/Leg ModeDescriptionF3 0F B8 /rPOPCNT r16, r/m16RMValidValidPOPCNT on r/m16F3 0F B8 /rPOPCNT r32, r/m32RMValidValidPOPCNT on r/m32F3 REX.W 0F B8 /rPOPCNT r64, r/m64RMValidN.E.POPCNT on r/m64Op/EnOperand 1Operand 2Operand 3Operand 4RMModRM:reg (w)ModRM:r/m (r)NANA

image/svg+xmlVirtual 8086 Mode Exceptions#GP(0)If any part of the operand lies outside of the effective address space from 0 to 0FFFFH.#SS(0)If a memory operand effective address is outside the SS segment limit.#PF (fault-code)For a page fault.#AC(0)If an unaligned memory reference is made while alignment checking is enabled.#UDIf CPUID.01H:ECX.POPCNT [Bit 23] = 0.If LOCK prefix is used.Compatibility Mode ExceptionsSame exceptions as in Protected Mode.64-Bit Mode Exceptions#GP(0)If the memory address is in a non-canonical form.#SS(0)If a memory address referencing the SS segment is in a non-canonical form.#PF (fault-code)For a page fault.#AC(0)If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.#UDIf CPUID.01H:ECX.POPCNT [Bit 23] = 0.If LOCK prefix is used.

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