Signed Most Significant Word Multiply Subtract multiplies two signed 32-bit values, subtracts the result from a 32-bit accumulate value that is shifted left by 32 bits, and extracts the most significant 32 bits of the result of that subtraction.
Optionally, the instruction can specify that the result of the instruction is rounded instead of being truncated. In this case, the constant 0x80000000 is added to the result of the subtraction before the high word is extracted.
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 | 1 | 1 | 1 | 0 | 1 | 0 | 1 | Rd | Ra | Rm | 1 | 1 | R | 1 | Rn | |||||||||||||||
| cond | |||||||||||||||||||||||||||||||
constant d = UInt(Rd); constant n = UInt(Rn); constant m = UInt(Rm); constant a = UInt(Ra); constant round = (R == '1'); if d == 15 || n == 15 || m == 15 || a == 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 | 1 | 1 | 0 | Rn | Ra | Rd | 0 | 0 | 0 | R | Rm | ||||||||||||
constant d = UInt(Rd); constant n = UInt(Rn); constant m = UInt(Rm); constant a = UInt(Ra); constant round = (R == '1'); // Armv8-A removes UNPREDICTABLE for R13 if d == 15 || n == 15 || m == 15 || a == 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, encoded in the "Rn" field. |
| <Rm> |
Is the second general-purpose source register holding the multiplier, encoded in the "Rm" field. |
| <Ra> |
Is the third general-purpose source register holding the addend, encoded in the "Ra" field. |
if ConditionPassed() then EncodingSpecificOperations(); integer result = (SInt(R[a]) << 32) - SInt(R[n]) * SInt(R[m]); if round then result = result + 0x80000000; R[d] = result<63:32>;
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_32, pseudocode v2024-12_rel ; Build timestamp: 2024-12-16T10:54
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