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TEST -- Logical Compare

Opcode       Instruction       Clocks   Description

A8   ib      TEST AL,imm8      2        AND immediate byte with AL
A9   iw      TEST AX,imm16     2        AND immediate word with AX
A9   id      TEST EAX,imm32    2        AND immediate dword with EAX
F6   /0 ib   TEST r/m8,imm8    2/5      AND immediate byte with r/m byte
F7   /0 iw   TEST r/m16,imm16  2/5      AND immediate word with r/m word
F7   /0 id   TEST r/m32,imm32  2/5      AND immediate dword with r/m dword
84   /r      TEST r/m8,r8      2/5      AND byte register with r/m byte
85   /r      TEST r/m16,r16    2/5      AND word register with r/m word
85   /r      TEST r/m32,r32    2/5      AND dword register with r/m dword

Operation

DEST := LeftSRC AND RightSRC;
CF := 0;
OF := 0;

Description

TEST computes the bit-wise logical AND of its two operands. Each bit of the result is 1 if both of the corresponding bits of the operands are 1; otherwise, each bit is 0. The result of the operation is discarded and only the flags are modified.

Flags Affected

OF := 0, CF := 0; SF, ZF, and PF as described in Appendix C

Protected Mode Exceptions

#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 fault

Real Address Mode Exceptions

Interrupt 13 if any part of the operand would lie outside of the effective address space from 0 to 0FFFFH

Virtual 8086 Mode Exceptions

Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault

up: Chapter 17 -- 80386 Instruction Set
prev: SUB Integer Subtraction
next: VERR Verify a Segment for Reading or Writing