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USDOT (by element)

Dot Product index form with unsigned and signed integers. This instruction performs the dot product of the four unsigned 8-bit integer values in each 32-bit element of the first source register with the four signed 8-bit integer values in an indexed 32-bit element of the second source register, accumulating the result into the corresponding 32-bit element of the destination register.

From Armv8.2 to Armv8.5, this is an optional instruction. From Armv8.6 it is mandatory for implementations that include Advanced SIMD to support it. ID_AA64ISAR1_EL1.I8MM indicates whether this instruction is supported.




USDOT <Vd>.<Ta>, <Vn>.<Tb>, <Vm>.4B[<index>]

if !HaveInt8MatMulExt() then UNDEFINED;
boolean op1_unsigned = (US == '1');
boolean op2_unsigned = (US == '0');
integer n = UInt(Rn);
integer m = UInt(M:Rm);
integer d = UInt(Rd);
integer i = UInt(H:L);
integer datasize = if Q == '1' then 128 else 64;
integer elements = datasize DIV 32;

Assembler Symbols


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

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

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


Is the immediate index of a quadtuplet of four 8-bit elements in the range 0 to 3, encoded in the "H:L" fields.


bits(datasize) operand1 = V[n];
bits(128)      operand2 = V[m];
bits(datasize) operand3 = V[d];
bits(datasize) result;

for e = 0 to elements-1
    bits(32) res = Elem[operand3, e, 32];
    for b = 0 to 3
        integer element1 = Int(Elem[operand1, 4 * e + b, 8], op1_unsigned);
        integer element2 = Int(Elem[operand2, 4 * i + b, 8], op2_unsigned);
        res = res + element1 * element2;
    Elem[result, e, 32] = res;
V[d] = result;