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SDOT (vector)

Dot Product signed arithmetic (vector). This instruction performs the dot product of the four signed 8-bit elements in each 32-bit element of the first source register with the four signed 8-bit elements of the corresponding 32-bit element in the second source register, accumulating the result into the corresponding 32-bit element of the destination register.

Depending on the settings in the CPACR_EL1, CPTR_EL2, and CPTR_EL3 registers, and the current Security state and Exception level, an attempt to execute the instruction might be trapped.

In Armv8.2 and Armv8.3, this is an optional instruction. From Armv8.4 it is mandatory for all implementations to support it.

ID_AA64ISAR0_EL1.DP indicates whether this instruction is supported.

Vector
(Armv8.2)

313029282726252423222120191817161514131211109876543210
0Q001110size0Rm100101RnRd
U

Vector

SDOT <Vd>.<Ta>, <Vn>.<Tb>, <Vm>.<Tb>

if !HaveDOTPExt() then UNDEFINED;
if size != '10' then UNDEFINED;
boolean signed = (U == '0');
integer d = UInt(Rd);
integer n = UInt(Rn);
integer m = UInt(Rm);
integer esize = 8 << UInt(size);
integer datasize = if Q == '1' then 128 else 64;
integer elements = datasize DIV esize;

Assembler Symbols

<Vd>

Is the name of the SIMD&FP third source and destination register, encoded in the "Rd" field.

<Ta> Is an arrangement specifier, encoded in Q:
Q <Ta>
0 2S
1 4S
<Vn>

Is the name of the first SIMD&FP source register, encoded in the "Rn" field.

<Tb> Is an arrangement specifier, encoded in Q:
Q <Tb>
0 8B
1 16B
<Vm>

Is the name of the second SIMD&FP source register, encoded in the "Rm" field.

Operation

CheckFPAdvSIMDEnabled64();
bits(datasize) operand1 = V[n];
bits(datasize) operand2 = V[m];
bits(datasize) result;

result = V[d];
for e = 0 to elements-1
    integer res = 0;
    integer element1, element2;
    for i = 0 to 3
        if signed then
            element1 = SInt(Elem[operand1, 4*e+i, esize DIV 4]);
            element2 = SInt(Elem[operand2, 4*e+i, esize DIV 4]);
        else
            element1 = UInt(Elem[operand1, 4*e+i, esize DIV 4]);
            element2 = UInt(Elem[operand2, 4*e+i, esize DIV 4]);
        res = res + element1 * element2;
    Elem[result, e, esize] = Elem[result, e, esize] + res;
V[d] = result;