问题
Possible Duplicate:
C reverse bits in unsigned integer
How can I reverse a binary number only using binary operators?
E.g:
11100000 -> 00000111
00110100 -> 00101100
00111111 -> 11111100
回答1:
For this sort of thing I recommend that you take a look at the awesome page Bit Twiddling Hacks.
Here is just one example solution taken from that page:
Reverse the bits in a byte with 3 operations (64-bit multiply and modulus division)
unsigned char b; // reverse this (8-bit) byte b = (b * 0x0202020202ULL & 0x010884422010ULL) % 1023;
And as pointed out in the comments, here's another option:
Reverse an N-bit quantity in parallel in 5 * lg(N) operations
unsigned int v; // 32-bit word to reverse bit order // swap odd and even bits v = ((v >> 1) & 0x55555555) | ((v & 0x55555555) << 1); // swap consecutive pairs v = ((v >> 2) & 0x33333333) | ((v & 0x33333333) << 2); // swap nibbles ... v = ((v >> 4) & 0x0F0F0F0F) | ((v & 0x0F0F0F0F) << 4); // swap bytes v = ((v >> 8) & 0x00FF00FF) | ((v & 0x00FF00FF) << 8); // swap 2-byte long pairs v = ( v >> 16 ) | ( v << 16);
回答2:
Take a look at Bit Twiddling Hacks. There's an entire section on reversing bit sequences.
回答3:
You can see this website http://graphics.stanford.edu/~seander/bithacks.html
Reversing bit sequences
Reverse bits the obvious way
Reverse bits in word by lookup table
Reverse the bits in a byte with 3 operations (64-bit multiply and modulus division)
Reverse the bits in a byte with 4 operations (64-bit multiply, no division)
Reverse the bits in a byte with 7 operations (no 64-bit, only 32)
Reverse an N-bit quantity in parallel with 5 * lg(N) operations
来源：https://stackoverflow.com/questions/12903359/c-reverse-binary