5. Arithmetic instructions

5.1. Document conventions

Notation: Rd, Rm, Rn denote ARM registers R0-R7. immN denotes an immediate value having a width of N bits e.g. imm8, imm3. carry denotes the carry condition flag, not(carry) denotes its complement. In the case of instructions with more than one register argument, it is permissible for some to be identical. For example the following will add the contents of R0 to itself, placing the result in R0:

  • add(r0, r0, r0)

Arithmetic instructions affect the condition flags except when stated otherwise.

5.2. Addition

  • add(Rdn, imm8) Rdn = Rdn + imm8
  • add(Rd, Rn, imm3) Rd = Rn + imm3
  • add(Rd, Rn, Rm) Rd = Rn + Rm
  • adc(Rd, Rn) Rd = Rd + Rn + carry

5.3. Subtraction

  • sub(Rdn, imm8) Rdn = Rdn - imm8
  • sub(Rd, Rn, imm3) Rd = Rn - imm3
  • sub(Rd, Rn, Rm) Rd = Rn - Rm
  • sbc(Rd, Rn) Rd = Rd - Rn - not(carry)

5.4. Negation

  • neg(Rd, Rn) Rd = -Rn

5.5. Multiplication and division

  • mul(Rd, Rn) Rd = Rd * Rn

This produces a 32 bit result where the overflow bits are lost. The result may be treated as signed or unsigned according to the definition of the operands.

  • sdiv(Rd, Rn, Rm) Rd = Rn / Rm
  • udiv(Rd, Rn, Rm) Rd = Rn / Rm

These functions perform signed and unsigned division respectively. Condition flags are not affected.