# core.bitop

This module contains a collection of bit-level operations.
License:
Boost License 1.0.
Authors:
Don Clugston, Sean Kelly, Walter Bright
Copyright Don Clugston 2005 - 2009. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at ) http:
//www.boost.org/LICENSE_1_0.txt

int bsf(uint v);
  Scans the bits in v starting with bit 0, looking for the first set bit.
  Returns:
  The bit number of the first bit set. The return value is undefined if v is zero.
int bsr(uint v);
  Scans the bits in v from the most significant bit to the least significant bit, looking for the first set bit.
  Returns:
  The bit number of the first bit set. The return value is undefined if v is zero.
  Example:

       import core.bitop;

       int main()
       {
           uint v;
           int x;

           v = 0x21;
           x = bsf(v);
           printf("bsf(x%x) = %d\n", v, x);
           x = bsr(v);
           printf("bsr(x%x) = %d\n", v, x);
           return 0;
       }

  Output:
  bsf(x21) = 0
  bsr(x21) = 5
int bt(uint* p, uint bitnum);
  Tests the bit.
int btc(uint* p, uint bitnum);
  Tests and complements the bit.
int btr(uint* p, uint bitnum);
  Tests and resets (sets to 0) the bit.
int bts(uint* p, uint bitnum);
  Tests and sets the bit.
  Params:

  uint* p | a non-NULL pointer to an array of uints.
  index | a bit number, starting with bit 0 of p[0], and progressing. It addresses bits like the expression:
          p[index / (uint.sizeof*8)] & (1 << (index & ((uint.sizeof*8) - 1)))

  Returns:
  A non-zero value if the bit was set, and a zero if it was clear.
  Example:

          import core.bitop;

          int main()
          {
              uint array[2];

              array[0] = 2;
              array[1] = 0x100;

              printf("btc(array, 35) = %d\n", <b>btc</b>(array, 35));
              printf("array = [0]:x%x, [1]:x%x\n", array[0], array[1]);

              printf("btc(array, 35) = %d\n", <b>btc</b>(array, 35));
              printf("array = [0]:x%x, [1]:x%x\n", array[0], array[1]);

              printf("bts(array, 35) = %d\n", <b>bts</b>(array, 35));
              printf("array = [0]:x%x, [1]:x%x\n", array[0], array[1]);

              printf("btr(array, 35) = %d\n", <b>btr</b>(array, 35));
              printf("array = [0]:x%x, [1]:x%x\n", array[0], array[1]);

              printf("bt(array, 1) = %d\n", <b>bt</b>(array, 1));
              printf("array = [0]:x%x, [1]:x%x\n", array[0], array[1]);

              return 0;
          }

  Output:

          btc(array, 35) = 0
          array = [0]:x2, [1]:x108
          btc(array, 35) = -1
          array = [0]:x2, [1]:x100
          bts(array, 35) = 0
          array = [0]:x2, [1]:x108
          btr(array, 35) = -1
          array = [0]:x2, [1]:x100
          bt(array, 1) = -1
          array = [0]:x2, [1]:x100

uint bswap(uint v);
  Swaps bytes in a 4 byte uint end-to-end, i.e. byte 0 becomes byte 3, byte 1 becomes byte 2, byte 2 becomes byte 1, byte 3 becomes byte 0.
ubyte inp(uint port_address);
ushort inpw(uint port_address);
uint inpl(uint port_address);
  Reads I/O port at port_address.
ubyte outp(uint port_address, ubyte value);
ushort outpw(uint port_address, ushort value);
uint outpl(uint port_address, uint value);
  Writes and returns value to I/O port at port_address.
int popcnt(uint x);
  Calculates the number of set bits in a 32-bit integer.
uint bitswap(uint x);
  Reverses the order of bits in a 32-bit integer.

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