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Last update Sun Apr 19 16:54:14 2009

# std.intrinsic

These functions are built-in intrinsics to the compiler.

Intrinsic functions are functions built in to the compiler, usually to take advantage of specific CPU features that are inefficient to handle via external functions. The compiler's optimizer and code generator are fully integrated in with intrinsic functions, bringing to bear their full power on them. This can result in some surprising speedups.

License:
Public Domain

Authors:
Walter Bright

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 std.stdio;
       import std.intrinsic;

       int main()
       {
           uint v;
           int x;

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

  Output:
  bsf(x21) = 0
  bsr(x21) = 5

int bt(in 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.

  Parameters:

  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 std.stdio;
      import std.intrinsic;

      int main()
      {
          uint array[2];

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

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

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

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

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

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

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