DSP程序优化C循环的实例
- #define WORD_ALIGNED(x) (_nassert(((int)(x) & 0x3) == 0))
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/*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;
- }
- }
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