#define WORD_ALIGNED(x) (_nassert(((int)(x) & 0x3) == 0)) /*输入参数加上关键字restrict，内存独立声明，xptr yptr指向的区域不重合*/ void lesson3_c(short * restrict xptr, short * restrict yptr, short *zptr,                short *w_sum, int N) {     int i, w_vec1, w_vec2;     short w1, w2;           /*保证xptr yptr是四字节对齐的，编程者负责要保证这一点*/                                 WORD_ALIGNED(xptr);     WORD_ALIGNED(yptr);                                                                              w1 = zptr[0];     w2 = zptr[1];       /*最小循环20次，循环的次数是2的倍数*/     #pragma MUST_ITERATE(20, , 2);     for (i = 0; i < N; i++)     {         w_vec1 =  xptr * w1;         w_vec2 =  yptr * w2;         w_sum = (w_vec1 + w_vec2) >> 15;     } }