可以使用反向查找表优化循环。
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this
我从下面的代码采取的网址。
// Generate a lookup table for 32bit operating system
// using macro
#define R2(n) n, n + 2*64, n + 1*64, n + 3*64
#define R4(n) R2(n), R2(n + 2*16), R2(n + 1*16), R2(n + 3*16)
#define R6(n) R4(n), R4(n + 2*4 ), R4(n + 1*4 ), R4(n + 3*4 )
// Lookup table that store the reverse of each table
unsigned int lookuptable[256] = { R6(0), R6(2), R6(1), R6(3) };
/* Function to reverse bits of num */
int reverseBits(unsigned int num)
{
int reverse_num = 0;
// Reverse and then rearrange
// first chunk of 8 bits from right
reverse_num = lookuptable[ num & 0xff ]<<24 |
// second chunk of 8 bits from right
lookuptable[ (num >> 8) & 0xff ]<<16 |
lookuptable[ (num >> 16 )& 0xff ]<< 8 |
lookuptable[ (num >>24 ) & 0xff ] ;
return reverse_num;
}
