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.
It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 ) .
| 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| != 1111 | 0 | 0 | 0 | 1 | 0 | 1 | 1 | 0 | Rd | (0) | (0) | (0) | (0) | Rm | 1 | M | N | 0 | Rn | ||||||||||||
| cond | |||||||||||||||||||||||||||||||
constant d = UInt(Rd); constant n = UInt(Rn); constant m = UInt(Rm); constant n_high = (N == '1'); constant m_high = (M == '1'); if d == 15 || n == 15 || m == 15 then UNPREDICTABLE;
| 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | Rn | 1 | 1 | 1 | 1 | Rd | 0 | 0 | N | M | Rm | |||||||||
constant d = UInt(Rd); constant n = UInt(Rn); constant m = UInt(Rm); constant n_high = (N == '1'); constant m_high = (M == '1'); // Armv8-A removes UNPREDICTABLE for R13 if d == 15 || n == 15 || m == 15 then UNPREDICTABLE;
For more information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors.
| <c> |
| <q> |
| <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(); constant operand1 = if n_high then R[n]<31:16> else R[n]<15:0>; constant operand2 = if m_high then R[m]<31:16> else R[m]<15:0>; constant result = SInt(operand1) * SInt(operand2); R[d] = result<31:0>; // Signed overflow cannot occur
If CPSR.DIT is 1, this instruction has passed its condition execution check, and does not use R15 as either its source or destination:
Internal version only: isa v01_31, pseudocode v2024-03_rel ; Build timestamp: 2024-03-25T10:05
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