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# 8-bit vector API

group vect_s8_api

  Functions

  void vect_s8_is_negative(int8_t a[], const int8_t b[], const unsigned length)

    Determine whether each element of a signed 8-bit input vector are negative.

    Each element \(a_k\) of 8-bit output vector \(\bar a\) is set to 1 if the corresponding element \(b_k\) of 8-bit input vector \(\bar b\) is negative, and is set to 0 otherwise.

    `a[]` represents the 8-bit output vector \(\bar a\) , with the element `a[k]` representing \(a_k\) .

    `b[]` represents the 8-bit input vector \(\bar b\) , with the element `b[k]` representing \(b_k\) .

    `length` is the number of elements in `a[]` and `b[]`.

    Operation Performed

      \[\begin{split}\begin{aligned} & a_k \leftarrow \begin{cases} 1 & b_k < 0 \\ 0 & otherwise\end{cases} \\ & \qquad\text{ for }k\in 0\ ...\ (length-1) \end{aligned}\end{split}\]
    Parameters:

      - a – [out] Output vector \(\bar a\)

      - b – [in] Input vector \(\bar b\)

      - length – [in] Number of elements in \(\bar a\) and \(\bar b\)

    Throws ET_LOAD_STORE:

      Raised if `a` or `b` is not word-aligned (See Note: Vector Alignment)

  void mat_mul_s8_x_s8_yield_s32(split_acc_s32_t accumulators[], const int8_t matrix[], const int8_t input_vect[], const unsigned M_rows, const unsigned N_cols)

    Multiply-accumulate an 8-bit matrix by an 8-bit vector into 32-bit accumulators.

    This function multiplies an 8-bit \(M \times N\) matrix \(\bar W\) by an 8-bit \(N\) -element column vector \(\bar v\) and adds it to the 32-bit accumulator vector \(\bar a\) .

    `accumulators` is the output vector \(\bar a\) to which the product \(\bar W\times\bar v\) is accumulated. Note that the accumulators are encoded in a format native to the xcore VPU. To initialize the accumulator vector to zeros, just zero the memory.

    `matrix` is the matrix \(\bar W\) .

    `input_vect` is the vector \(\bar v\) .

    `matrix` and `input_vect` must both begin at a word-aligned offsets.

    `M_rows` and `N_rows` are the dimensions \(M\) and \(N\) of matrix \(\bar W\) . \(M\) must be a multiple of 16, and \(N\) must be a multiple of 32.

    The result of this multiplication is exact, so long as saturation does not occur.

    Parameters:

      - accumulators – [inout] The accumulator vector \(\bar a\)

      - matrix – [in] The weight matrix \(\bar W\)

      - input_vect – [in] The input vector \(\bar v\)

      - M_rows – [in] The number of rows \(M\) in matrix \(\bar W\)

      - N_cols – [in] The number of columns \(N\) in matrix \(\bar W\)

    Throws ET_LOAD_STORE:

      Raised if `matrix` or `input_vect` is not word-aligned (See Note: Vector Alignment)