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80386 Programmer's Reference Manual -- Opcode NEG

NEG -- Two's Complement Negation

Opcode	Instruction	Clocks	Description	Example
F6 /3	negb r/m8	2/6	Two's complement negate r/m byte	`negb %dl negb (%ebx,1) negb m8(%ebx,1) negb m8(%ebx,%ebp,1)`
F7 /3	negw r/m16	2/6	Two's complement negate r/m word	`negw %cx negw (%ebx,1) negw (%ebx,2) negw (%ebx,%ebp,1)`
F7 /3	negl r/m32	2/6	Two's complement negate r/m dword	`negl %ecx negl (%ebx,2) negl (%ebx,4) negl (%ebx,%ebp,1)`

Operation




IF r/m = 0 THEN CF := 0 ELSE CF := 1; FI;
r/m := - r/m;

Description

NEG replaces the value of a register or memory operand with its two's complement. The operand is subtracted from zero, and the result is placed in the operand.

The carry flag is set to 1, unless the operand is zero, in which case the carry flag is cleared to 0.

Flags Affected

CF as described above; OF, SF, ZF, and PF as described in Appendix C

Protected 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 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

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