SMULBB, SMULBT, SMULTB, SMULTT Signed Multiply (halfwords) Signed Multiply (halfwords) multiplies two signed 16-bit quantities, taken from either the bottom or the top half of their respective source registers. The other halves of these source registers are ignored. The 32-bit product is written to the destination register. No overflow is possible during this instruction. For more information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors. If CPSR.DIT is 1, this instruction has passed its condition execution check, and does not use R15 as either its source or destination: The execution time of this instruction is independent of:The values of the data supplied in any of its registers.The values of the NZCV flags. The response of this instruction to asynchronous exceptions does not vary based on:The values of the data supplied in any of its registers.The values of the NZCV flags. It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 ) . != 1111 0 0 0 1 0 1 1 0 (0) (0) (0) (0) 1 0 0 0 SMULBB{<c>}{<q>} {<Rd>,} <Rn>, <Rm> 1 0 SMULBT{<c>}{<q>} {<Rd>,} <Rn>, <Rm> 0 1 SMULTB{<c>}{<q>} {<Rd>,} <Rn>, <Rm> 1 1 SMULTT{<c>}{<q>} {<Rd>,} <Rn>, <Rm> d = UInt(Rd); n = UInt(Rn); m = UInt(Rm); n_high = (N == '1'); m_high = (M == '1'); if d == 15 || n == 15 || m == 15 then UNPREDICTABLE; 1 1 1 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 0 0 SMULBB{<c>}{<q>} {<Rd>,} <Rn>, <Rm> 0 1 SMULBT{<c>}{<q>} {<Rd>,} <Rn>, <Rm> 1 0 SMULTB{<c>}{<q>} {<Rd>,} <Rn>, <Rm> 1 1 SMULTT{<c>}{<q>} {<Rd>,} <Rn>, <Rm> d = UInt(Rd); n = UInt(Rn); m = UInt(Rm); n_high = (N == '1'); m_high = (M == '1'); if d == 15 || n == 15 || m == 15 then UNPREDICTABLE; // Armv8-A removes UNPREDICTABLE for R13 <c> See Standard assembler syntax fields. <q> See Standard assembler syntax fields. <Rd> Is the general-purpose destination register, encoded in the "Rd" field. <Rn> Is the first general-purpose source register holding the multiplicand in the bottom or top half (selected by <x>), encoded in the "Rn" field. <Rm> Is the second general-purpose source register holding the multiplier in the bottom or top half (selected by <y>), encoded in the "Rm" field. if ConditionPassed() then EncodingSpecificOperations(); operand1 = if n_high then R[n]<31:16> else R[n]<15:0>; operand2 = if m_high then R[m]<31:16> else R[m]<15:0>; result = SInt(operand1) * SInt(operand2); R[d] = result<31:0>; // Signed overflow cannot occur