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SMMLS, SMMLSR

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 ) .

A1

313029282726252423222120191817161514131211109876543210
!= 111101110101RdRaRm11R1Rn
cond

SMMLS (R == 0)

SMMLS{<c>}{<q>} <Rd>, <Rn>, <Rm>, <Ra>

SMMLSR (R == 1)

SMMLSR{<c>}{<q>} <Rd>, <Rn>, <Rm>, <Ra>

d = UInt(Rd);  n = UInt(Rn);  m = UInt(Rm);  a = UInt(Ra);  round = (R == '1');
if d == 15 || n == 15 || m == 15 || a == 15 then UNPREDICTABLE;

T1

15141312111098765432101514131211109876543210
111110110110RnRaRd000RRm

SMMLS (R == 0)

SMMLS{<c>}{<q>} <Rd>, <Rn>, <Rm>, <Ra>

SMMLSR (R == 1)

SMMLSR{<c>}{<q>} <Rd>, <Rn>, <Rm>, <Ra>

d = UInt(Rd);  n = UInt(Rn);  m = UInt(Rm);  a = UInt(Ra);  round = (R == '1');
if d == 15 || n == 15 || m == 15 || a == 15 then UNPREDICTABLE;
// Armv8-A removes UNPREDICTABLE for R13

For more information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors.

Assembler Symbols

<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, 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.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    result = (SInt(R[a]) << 32) - SInt(R[n]) * SInt(R[m]);
    if round then result = result + 0x80000000;
    R[d] = result<63:32>;

Operational information

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.
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