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# core.bitop

This module contains a collection of bit-level operations.
License:
Boost License 1.0
Authors:
Don Clugston, Sean Kelly, Walter Bright, Alex Rønne Petersen, Thomas Stuart Bockman

Source core/bitop.d

pure nothrow @nogc @safe int `bsf`(uint `v`);
pure nothrow @nogc @safe int `bsf`(ulong `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.
  Examples:

      assert(bsf(0x21) == 0);
      assert(bsf(ulong.max << 39) == 39);

pure nothrow @nogc @safe int `bsr`(uint `v`);
pure nothrow @nogc @safe int `bsr`(ulong `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.
  Examples:

      assert(bsr(0x21) == 5);
      assert(bsr((ulong.max >> 15) - 1) == 48);

pure nothrow @nogc @system int `bt`(scope const size_t* `p`, size_t `bitnum`);
  Tests the bit. (No longer an intrisic - the compiler recognizes the patterns in the body.)
  Examples:

      size_t[2] array;

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

      assert(bt(array.ptr, 1));
      assert(array[0] == 2);
      assert(array[1] == 0x100);

pure nothrow @nogc @system int `btc`(size_t* `p`, size_t `bitnum`);
  Tests and complements the bit.
pure nothrow @nogc @system int `btr`(size_t* `p`, size_t `bitnum`);
  Tests and resets (sets to 0) the bit.
pure nothrow @nogc @system int `bts`(size_t* `p`, size_t `bitnum`);
  Tests and sets the bit.
  Parameters:

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

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

      size_t[2] array;

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

      assert(btc(array.ptr, 35) == 0);
      if (size_t.sizeof == 8)
      {
          assert(array[0] == 0x8_0000_0002);
          assert(array[1] == 0x100);
      }
      else
      {
          assert(array[0] == 2);
          assert(array[1] == 0x108);
      }

      assert(btc(array.ptr, 35));
      assert(array[0] == 2);
      assert(array[1] == 0x100);

      assert(bts(array.ptr, 35) == 0);
      if (size_t.sizeof == 8)
      {
          assert(array[0] == 0x8_0000_0002);
          assert(array[1] == 0x100);
      }
      else
      {
          assert(array[0] == 2);
          assert(array[1] == 0x108);
      }

      assert(btr(array.ptr, 35));
      assert(array[0] == 2);
      assert(array[1] == 0x100);

struct `BitRange`;
  Range over bit set. Each element is the bit number that is set.
  This is more efficient than testing each bit in a sparsely populated bit set. Note that the first bit in the bit set would be bit 0.
  Examples:

      import core.stdc.stdlib : malloc, free;
      import core.stdc.string : memset;

      // initialize a bit array
      enum nBytes = (100 + BitRange.bitsPerWord - 1) / 8;
      size_t *bitArr = cast(size_t *)malloc(nBytes);
      scope(exit) free(bitArr);
      memset(bitArr, 0, nBytes);

      // set some bits
      bts(bitArr, 48);
      bts(bitArr, 24);
      bts(bitArr, 95);
      bts(bitArr, 78);

      enum sum = 48 + 24 + 95 + 78;

      // iterate
      size_t testSum;
      size_t nBits;
      foreach (b; BitRange(bitArr, 100))
      {
          testSum += b;
          ++nBits;
      }

      assert(testSum == sum);
      assert(nBits == 4);

  enum ulong `bitsPerWord`;
    Number of bits in each size_t
  pure nothrow @nogc @system this(const(size_t)* `bitarr`, size_t `numBits`);
    Construct a BitRange.
    Parameters:

    const(size_t)* `bitarr` | The array of bits to iterate over
    size_t `numBits` | The total number of valid bits in the given bit array

  pure nothrow @nogc @safe size_t `front`();
  const pure nothrow @nogc @safe bool `empty`();
  pure nothrow @nogc @system void `popFront`();
    Range functions
pure nothrow @nogc @safe ushort `byteswap`(ushort `x`);
  Swaps bytes in a 2 byte ushort.
  Parameters:

  ushort `x` | value

  Returns:
  `x` with bytes swapped
  Examples:

      assert(byteswap(cast(ushort)0xF234) == 0x34F2);
      static ushort xx = 0xF234;
      assert(byteswap(xx) == 0x34F2);

pure nothrow @nogc @safe 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.
  Examples:

      assert(bswap(0x01020304u) == 0x04030201u);
      static uint xx = 0x10203040u;
      assert(bswap(xx) == 0x40302010u);

pure nothrow @nogc @safe ulong `bswap`(ulong `v`);
  Swaps bytes in an 8 byte ulong end-to-end, i.e. byte 0 becomes byte 7, byte 1 becomes byte 6, etc. This is meant to be recognized by the compiler as an intrinsic.
  Examples:

      assert(bswap(0x01020304_05060708uL) == 0x08070605_04030201uL);
      static ulong xx = 0x10203040_50607080uL;
      assert(bswap(xx) == 0x80706050_40302010uL);

nothrow @nogc @system ubyte `inp`(uint `port_address`);
nothrow @nogc @system ushort `inpw`(uint `port_address`);
nothrow @nogc @system uint `inpl`(uint `port_address`);
  Reads I/O port at port_address.
nothrow @nogc @system ubyte `outp`(uint `port_address`, ubyte `value`);
nothrow @nogc @system ushort `outpw`(uint `port_address`, ushort `value`);
nothrow @nogc @system uint `outpl`(uint `port_address`, uint `value`);
  Writes and returns value to I/O port at port_address.
pure nothrow @nogc @safe int `popcnt`(uint `x`);
pure nothrow @nogc @safe int `popcnt`(ulong `x`);
  Calculates the number of set bits in an integer.
pure nothrow @nogc @safe ushort `_popcnt`(ushort `x`);
pure nothrow @nogc @safe int `_popcnt`(uint `x`);
pure nothrow @nogc @safe int `_popcnt`(ulong `x`);
  Calculates the number of set bits in an integer using the X86 SSE4 POPCNT instruction. POPCNT is not available on all X86 CPUs.
pure nothrow @nogc @safe uint `bitswap`(uint `x`);
  Reverses the order of bits in a 32-bit integer.
pure nothrow @nogc @safe ulong `bitswap`(ulong `x`);
  Reverses the order of bits in a 64-bit integer.
pure T `rol`(T)(const T `value`, const uint `count`)
if (__traits(isIntegral, T) && __traits(isUnsigned, T));
pure T `ror`(T)(const T `value`, const uint `count`)
if (__traits(isIntegral, T) && __traits(isUnsigned, T));
pure T `rol`(uint count, T)(const T `value`)
if (__traits(isIntegral, T) && __traits(isUnsigned, T));
pure T `ror`(uint count, T)(const T `value`)
if (__traits(isIntegral, T) && __traits(isUnsigned, T));
  Bitwise rotate `value` left (`rol`) or right (`ror`) by `count` bit positions.
  Examples:

      ubyte a = 0b11110000U;
      ulong b = ~1UL;

      assert(rol(a, 1) == 0b11100001);
      assert(ror(a, 1) == 0b01111000);
      assert(rol(a, 3) == 0b10000111);
      assert(ror(a, 3) == 0b00011110);

      assert(rol(a, 0) == a);
      assert(ror(a, 0) == a);

      assert(rol(b, 63) == ~(1UL << 63));
      assert(ror(b, 63) == ~2UL);

      assert(rol!3(a) == 0b10000111);
      assert(ror!3(a) == 0b00011110);

      enum c = rol(uint(1), 0);
      enum d = ror(uint(1), 0);
      assert(c == uint(1));
      assert(d == uint(1));

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