32×32→32 Multiply Instructions

<operation>

• MUL – Multiply
  • Rd := Rm × Rs
• MLA – Multiply with Accumulate
  • Rd := Rn + (Rm × Rs)

The multiply instructions produce the same result for both signed and unsigned values.

Historical note: Prior to ARMv4 specifying the same register for Rd and Rm had potentially unpredictable results.

32×32→64 Multiply Instructions

64-bit result output into two registers.

<operation>

• UMULL – Unsigned Multiply Long
  • RdHi, RdLo := Rm × Rs
• UMLAL – Unsigned Multiply with Accumlate Long
  • RdHi, RdLo := RdHi,RdLo + (Rm × Rs)
• SMULL – Signed Multiply Long
  • RdHi, RdLo := Rm × Rs
• SMLAL – Signed Multiply with Accumlate Long
  • RdHi, RdLo := RdHi,RdLo + (Rm × Rs)

Note that they have the same form, but they treat the sign bit differently.