Introduction to ARM

Arithmetic

<operation>{cond}{S} Rd,Rn,<Operand2>

<operation>

ADD – add: Rd := Rn + Operand2
ADC – add with carry: Rd := Rn + Operand2 + Carry
SUB – subtract: Rd := Rn − Operand2
SBC – subtract with carry: Rd := Rn − Operand2 − NOT(Carry)
RSB – reverse subtract: Rd := Operand2 − Rn
RSC – reverse subtract with carry: Rd := Operand2 − Rn − NOT(Carry)

Examples

ADD r0, r1, r2: R0 = R1 + R2
SUB r5, r3, #10: R5 = R3 − 10
RSB r2, r5, #0xFF00: R2 = 0xFF00 − R5

Remarks

RSB and RSC subtract in reverse order (e.g. y − x not x − y).

Multiplication has a different format and is described later.

There is no divide instruction – the compiler uses a run-time library function or shifts to perform division.

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