EOR

EOR

Instruction	EOR[S]
Function	Logically Exclusive OR two values
Category	Data processing
ARM family	All
Notes	-

EOR[S] : bitwise Exclusive OR

EOR will perform a logical, bitwise, Exclusive OR between the two operands, placing the result in the destination register; this is useful for inverting certain bits. Operand 1 is a register, operand 2 can be a register, shifted register, or an immediate value (which may be shifted. If the S bit is set (ANDS), the N and Z flags are set according to the result, the C flag is set according to the shift (if used), and the V flag remains unaltered.

EOR is useful for inverting bits in a bitfield. For each bit, EORing with 1 will invert the bit, and EORing with 0 will leave it as it was.

This instruction is the same as the one called XOR on some other platforms.

Syntax

  EOR<suffix>  <dest>, <op 1>, <op 2>

Function

  dest = op_1 EOR op_2

EOR sets the result bit upon either, but not both of the input bits being the same.

Truth table:

op_1 bit	op_2 bit	Result bit
0	0	0
0	1	1
1	0	1
1	1	0

Example

  EOR  R0, R0, #3  ; Invert bits zero and one of R0.
  EORS R0, R0, #3  ; As above, but also updates status flags

Technical

The instruction bit pattern is as follows:

31 - 28	27	26	25	24 - 21	20	19 - 16	15 - 12	11 - 0
condition	0	0	I	0 0 0 1	S	op_1	dest	op_2/shift

Note: If the I bit is zero, and bits 4 and 7 are both one (with bits 5,6 zero), the instruction is MLA, not EOR.