SubGrad
=================

计算逐元素减法（Sub）操作的梯度。该算子是 Sub 算子的反向传播（backward pass）部分，支持广播。

.. math::

    \text{dx1} = \frac{\partial L}{\partial X1} = \frac{\partial L}{\partial Y} \times 1 = \frac{\partial L}{\partial Y}

.. math::

    \text{dx2} = \frac{\partial L}{\partial X2} = \frac{\partial L}{\partial Y} \times (-1) = -\frac{\partial L}{\partial Y}

其中对于前向操作 :math:`Y = X1 - X2`，`dy` 是来自后一层的上游梯度，`dx1` 和 `dx2` 分别是对 `X1` 和 `X2` 的梯度。


输入：
    - **dy** - 上游梯度数据地址（即 :math:`\frac{\partial L}{\partial Y}`）。
    - **params** - 参数打包成数组：
        - **dx1_dims** - 前向传播时第一个输入 `x1` 的维度信息数组（int*）。
        - **dx2_dims** - 前向传播时第二个输入 `x2` 的维度信息数组（int*）。
        - **dy_dims** - 上游梯度 `dy` 的维度信息数组（int*）。
        - **num_dims** - 维度数（int）。
        - **temp_space** - 临时空间地址，大小为 ``2 * num_dims * 4`` 字节。
    - **core_mask** - 核掩码（int），仅共享存储版本需要。

输出：
    - **dx1** - 对 `x1` 的梯度数据地址。
    - **dx2** - 对 `x2` 的梯度数据地址。

支持平台：
    ``FT78NE``
    ``MT7004``

.. note::
    - MT7004 支持fp16, fp32
    - FT78NE 支持fp32
    - 当输入张量被广播时，算子会自动处理广播维度的梯度累加

**共享存储版本:**

.. c:function:: void hp_sub_grad_s(half* dy, half* dx1, half* dx2, long long *params, int core_mask)
.. c:function:: void fp_sub_grad_s(float* dy, float* dx1, float* dx2, long long *params, int core_mask)

**C调用示例：**

.. code-block:: c
    :linenos:
    :emphasize-lines: 38

    //MT7004示例
    #include <stdio.h>
    #include <subgrad.h>

    int main(int argc, char* argv[]) {
        float *dy = (float *)0x81000000;
        float *dx1 = (float *)0x82000000;
        float *dx2 = (float *)0x83000000;
        float *checkdx1 = (float *)0x84000000;
        float *checkdx2 = (float *)0x85000000;
        int *tempsapce = (int *)0x86000000;
        
        srand(seed++);
        int i;
       
        // same shape
        int dx1_dims[] = {16, 16, 64};  // 2x2
        int dx2_dims[] = {1, 16, 64};  // 2x2
        int dy_dims[] = {16, 16, 64};  // 2x2
        int num_dims = 3;
        
        int dx1_num = get_total_elements(num_dims, dx1_dims);  
        int dx2_num = get_total_elements(num_dims, dx2_dims);
        int dy_num  = get_total_elements(num_dims, dy_dims);


        for (i = 0; i < dy_num; ++i) {
            dy[i] = (float)(rand() % 100) / 10.0f;
        }

        long long params[17];
        params[0] = (unsigned long long)dx1_dims;
        params[1] = (unsigned long long)dx2_dims;
        params[2] = (unsigned long long)dy_dims;
        params[3] = (unsigned long long)num_dims;
        params[4] = (unsigned long long)tempsapce;
        int core_mask = 0x0f;
        fp_sub_grad_s(dy, dx1, dx2, params, core_mask);
        return 0;
        
        return 0;
    }

**私有存储版本:**

.. c:function:: void hp_sub_grad_p(half* dy, half* dx1, half* dx2, long long *params)
.. c:function:: void fp_sub_grad_p(float* dy, float* dx1, float* dx2, long long *params)

**C调用示例：**

.. code-block:: c
    :linenos:
    :emphasize-lines: 38

    //MT7004示例
    #include <stdio.h>
    #include <subgrad.h>

    int main(int argc, char* argv[]) {
        float *dy = (float *)0x10010000;
        float *dx1 = (float *)0x10020000;
        float *dx2 = (float *)0x10030000;
        float *checkdx1 = (float *)0x10040000;
        float *checkdx2 = (float *)0x10050000;
        int *tempsapce = (int *)0x10060000;
        
        srand(seed++);
        int i;
       
        // same shape
        int dx1_dims[] = {16, 16, 64};  // 2x2
        int dx2_dims[] = {1, 16, 64};  // 2x2
        int dy_dims[] = {16, 16, 64};  // 2x2
        int num_dims = 3;
        
        int dx1_num = get_total_elements(num_dims, dx1_dims);  
        int dx2_num = get_total_elements(num_dims, dx2_dims);
        int dy_num  = get_total_elements(num_dims, dy_dims);


        for (i = 0; i < dy_num; ++i) {
            dy[i] = (float)(rand() % 100) / 10.0f;
        }

        long long params[17];
        params[0] = (unsigned long long)dx1_dims;
        params[1] = (unsigned long long)dx2_dims;
        params[2] = (unsigned long long)dy_dims;
        params[3] = (unsigned long long)num_dims;
        params[4] = (unsigned long long)tempsapce;

        fp_sub_grad_p(dy, dx1, dx2, params);

        return 0;
    }