## Reverse Bit Operations

## Reverse Bit Operations

(OP)

Hi,

I am looking for a C++ function to reverse the bits of a variable. For example, assume testvar = 11100110, then reverse(testvar) = 01100111. Does anyone know of such a function? Thanks.

I am looking for a C++ function to reverse the bits of a variable. For example, assume testvar = 11100110, then reverse(testvar) = 01100111. Does anyone know of such a function? Thanks.

## RE: Reverse Bit Operations

## RE: Reverse Bit Operations

## RE: Reverse Bit Operations

## RE: Reverse Bit Operations

You may use more sofisticated approach with byte by byte substitution too.

Alas, no binary constants with b suffix in C++...

## RE: Reverse Bit Operations

## RE: Reverse Bit Operations

## RE: Reverse Bit Operations

## RE: Reverse Bit Operations

htt

--

If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.

## RE: Reverse Bit Operations

## CODE

{

0x00,0x80,0x40,0xC0,0x20,0xA0,0x60,0xE0,0x10,0x90,0x50,0xD0,0x30,0xB0,0x70,0xF0,

0x08,0x88,0x48,0xC8,0x28,0xA8,0x68,0xE8,0x18,0x98,0x58,0xD8,0x38,0xB8,0x78,0xF8,

0x04,0x84,0x44,0xC4,0x24,0xA4,0x64,0xE4,0x14,0x94,0x54,0xD4,0x34,0xB4,0x74,0xF4,

0x0C,0x8C,0x4C,0xCC,0x2C,0xAC,0x6C,0xEC,0x1C,0x9C,0x5C,0xDC,0x3C,0xBC,0x7C,0xFC,

0x02,0x82,0x42,0xC2,0x22,0xA2,0x62,0xE2,0x12,0x92,0x52,0xD2,0x32,0xB2,0x72,0xF2,

0x0A,0x8A,0x4A,0xCA,0x2A,0xAA,0x6A,0xEA,0x1A,0x9A,0x5A,0xDA,0x3A,0xBA,0x7A,0xFA,

0x06,0x86,0x46,0xC6,0x26,0xA6,0x66,0xE6,0x16,0x96,0x56,0xD6,0x36,0xB6,0x76,0xF6,

0x0E,0x8E,0x4E,0xCE,0x2E,0xAE,0x6E,0xEE,0x1E,0x9E,0x5E,0xDE,0x3E,0xBE,0x7E,0xFE,

0x01,0x81,0x41,0xC1,0x21,0xA1,0x61,0xE1,0x11,0x91,0x51,0xD1,0x31,0xB1,0x71,0xF1,

0x09,0x89,0x49,0xC9,0x29,0xA9,0x69,0xE9,0x19,0x99,0x59,0xD9,0x39,0xB9,0x79,0xF9,

0x05,0x85,0x45,0xC5,0x25,0xA5,0x65,0xE5,0x15,0x95,0x55,0xD5,0x35,0xB5,0x75,0xF5,

0x0D,0x8D,0x4D,0xCD,0x2D,0xAD,0x6D,0xED,0x1D,0x9D,0x5D,0xDD,0x3D,0xBD,0x7D,0xFD,

0x03,0x83,0x43,0xC3,0x23,0xA3,0x63,0xE3,0x13,0x93,0x53,0xD3,0x33,0xB3,0x73,0xF3,

0x0B,0x8B,0x4B,0xCB,0x2B,0xAB,0x6B,0xEB,0x1B,0x9B,0x5B,0xDB,0x3B,0xBB,0x7B,0xFB,

0x07,0x87,0x47,0xC7,0x27,0xA7,0x67,0xE7,0x17,0x97,0x57,0xD7,0x37,0xB7,0x77,0xF7,

0x0F,0x8F,0x4F,0xCF,0x2F,0xAF,0x6F,0xEF,0x1F,0x9F,0x5F,0xDF,0x3F,0xBF,0x7F,0xFF,

};

/* this routine ignores byte structure (and addressing scheme) */

unsigned int revbits(unsigned int u)

{

int i, j, k;

unsigned int a, b;

unsigned int r = 0;

static int n;

static unsigned int uu = 0x100u;

/* octets per unsigned int?

it's interesting: can't calc with preprocessor!

*/

if (uu) /* the 1st call... */

for (n = 2; uu <<= 8; ++n) /* not thread-safe code! */

;

k = n;

for (i = 0, j = 8*(n-1); k > 1; k -= 2, i += 8, j -=8)

{

a = rb[(u >> i)&0xFFu];

b = rb[(u >> j)&0xFFu];

r |= (b << i);

r |= (a << j); /* next two reverted octets swapped */

}

if (k) /* (now exotic system with odd num of octets per uint;) */

r |= (rb[(u >> i)&0xFFu] << i);

return r;

}

## RE: Reverse Bit Operations