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/** @file bitmath_func.hpp Functions related to bit mathematics. */
#ifndef BITMATH_FUNC_HPP
#define BITMATH_FUNC_HPP
/**
* Fetch n bits from x, started at bit s.
*
* This function can be used to fetch n bits from the value x. The
* s value set the startposition to read. The startposition is
* count from the LSB and starts at 0. The result starts at a
* LSB, as this isn't just an and-bitmask but also some
* bit-shifting operations. GB(0xFF, 2, 1) will so
* return 0x01 (0000 0001) instead of
* 0x04 (0000 0100).
*
* @param x The value to read some bits.
* @param s The startposition to read some bits.
* @param n The number of bits to read.
* @return The selected bits, aligned to a LSB.
*/
template <typename T>
static FORCEINLINE uint GB(const T x, const uint8 s, const uint8 n)
{
return (x >> s) & ((1U << n) - 1);
}
/** Set \a n bits in \a x starting at bit \a s to \a d
*
* This function sets \a n bits from \a x which started as bit \a s to the value of
* \a d. The parameters \a x, \a s and \a n works the same as the parameters of
* #GB. The result is saved in \a x again. Unused bits in the window
* provided by n are set to 0 if the value of \a d isn't "big" enough.
* This is not a bug, its a feature.
*
* @note Parameter \a x must be a variable as the result is saved there.
* @note To avoid unexpecting results the value of \a d should not use more
* space as the provided space of \a n bits (log2)
* @param x The variable to change some bits
* @param s The startposition for the new bits
* @param n The size/window for the new bits
* @param d The actually new bits to save in the defined position.
* @return The new value of \a x
*/
template <typename T, typename U>
static FORCEINLINE T SB(T &x, const uint8 s, const uint8 n, const U d)
{
x &= (T)(~(((1U << n) - 1) << s));
x |= (T)(d << s);
return x;
}
/** Add i to n bits of x starting at bit s.
*
* This add the value of i on n bits of x starting at bit s. The parameters x,
* s, i are similar to #GB besides x must be a variable as the result are
* saved there. An overflow does not affect the following bits of the given
* bit window and is simply ignored.
*
* @note Parameter x must be a variable as the result is saved there.
* @param x The variable to add some bits at some position
* @param s The startposition of the addition
* @param n The size/window for the addition
* @param i The value to add at the given startposition in the given window.
* @return The new value of x
*/
template <typename T, typename U>
static FORCEINLINE T AB(T &x, const uint8 s, const uint8 n, const U i)
{
const T mask = (T)(((1U << n) - 1) << s);
x = (T)((x & ~mask) | ((x + (i << s)) & mask));
return x;
}
/**
* Checks if a bit in a value is set.
*
* This function checks if a bit inside a value is set or not.
* The y value specific the position of the bit, started at the
* LSB and count from 0.
*
* @param x The value to check
* @param y The position of the bit to check, started from the LSB
* @return True if the bit is set, false else.
*/
template <typename T>
static FORCEINLINE bool HasBit(const T x, const uint8 y)
{
return (x & ((T)1U << y)) != 0;
}
/**
* Check several bits in a value.
*
* This macro checks if a value contains at least one bit of an other
* value.
*
* @param x The first value
* @param y The second value
* @return True if at least one bit is set in both values, false else.
*/
#define HASBITS(x, y) (((x) & (y)) != 0)
/**
* Set a bit in a variable.
*
* This function sets a bit in a variable. The variable is changed
* and the value is also returned. Parameter y defines the bit and
* starts at the LSB with 0.
*
* @param x The variable to set a bit
* @param y The bit position to set
* @return The new value of the old value with the bit set
*/
template <typename T>
static FORCEINLINE T SetBit(T &x, const uint8 y)
{
return x = (T)(x | (T)(1U << y));
}
/**
* Sets several bits in a variable.
*
* This macro sets several bits in a variable. The bits to set are provided
* by a value. The new value is also returned.
*
* @param x The variable to set some bits
* @param y The value with set bits for setting them in the variable
* @return The new value of x
*/
#define SETBITS(x, y) ((x) |= (y))
/**
* Clears a bit in a variable.
*
* This function clears a bit in a variable. The variable is
* changed and the value is also returned. Parameter y defines the bit
* to clear and starts at the LSB with 0.
*
* @param x The variable to clear the bit
* @param y The bit position to clear
* @return The new value of the old value with the bit cleared
*/
template <typename T>
static FORCEINLINE T ClrBit(T &x, const uint8 y)
{
return x = (T)(x & ~((T)1U << y));
}
/**
* Clears several bits in a variable.
*
* This macro clears several bits in a variable. The bits to clear are
* provided by a value. The new value is also returned.
*
* @param x The variable to clear some bits
* @param y The value with set bits for clearing them in the variable
* @return The new value of x
*/
#define CLRBITS(x, y) ((x) &= ~(y))
/**
* Toggles a bit in a variable.
*
* This function toggles a bit in a variable. The variable is
* changed and the value is also returned. Parameter y defines the bit
* to toggle and starts at the LSB with 0.
*
* @param x The varliable to toggle the bit
* @param y The bit position to toggle
* @return The new value of the old value with the bit toggled
*/
template <typename T>
static FORCEINLINE T ToggleBit(T &x, const uint8 y)
{
return x = (T)(x ^ (T)(1U << y));
}
/** Lookup table to check which bit is set in a 6 bit variable */
extern const uint8 _ffb_64[64];
/**
* Returns the first occure of a bit in a 6-bit value (from right).
*
* Returns the position of the first bit that is not zero, counted from the
* LSB. Ie, 110100 returns 2, 000001 returns 0, etc. When x == 0 returns
* 0.
*
* @param x The 6-bit value to check the first zero-bit
* @return The first position of a bit started from the LSB or 0 if x is 0.
*/
#define FIND_FIRST_BIT(x) _ffb_64[(x)]
/**
* Finds the position of the first bit in an integer.
*
* This function returns the position of the first bit set in the
* integer. It does only check the bits of the bitmask
* 0x3F3F (0011111100111111) and checks only the
* bits of the bitmask 0x3F00 if and only if the
* lower part 0x00FF is 0. This results the bits at 0x00C0 must
* be also zero to check the bits at 0x3F00.
*
* @param value The value to check the first bits
* @return The position of the first bit which is set
* @see FIND_FIRST_BIT
*/
static FORCEINLINE uint8 FindFirstBit2x64(const int value)
{
if ((value & 0xFF) == 0) {
return FIND_FIRST_BIT((value >> 8) & 0x3F) + 8;
} else {
return FIND_FIRST_BIT(value & 0x3F);
}
}
uint8 FindFirstBit(uint32 x);
uint8 FindLastBit(uint64 x);
/**
* Clear the first bit in an integer.
*
* This function returns a value where the first bit (from LSB)
* is cleared.
* So, 110100 returns 110000, 000001 returns 000000, etc.
*
* @param value The value to clear the first bit
* @return The new value with the first bit cleared
*/
template <typename T>
static FORCEINLINE T KillFirstBit(T value)
{
return value &= (T)(value - 1);
}
/**
* Counts the number of set bits in a variable.
*
* @param value the value to count the number of bits in.
* @return the number of bits.
*/
template <typename T>
static inline uint CountBits(T value)
{
uint num;
/* This loop is only called once for every bit set by clearing the lowest
* bit in each loop. The number of bits is therefore equal to the number of
* times the loop was called. It was found at the following website:
* http://graphics.stanford.edu/~seander/bithacks.html */
for (num = 0; value != 0; num++) {
value &= (T)(value - 1);
}
return num;
}
/**
* ROtate x Left by n
*
* @note Assumes a byte has 8 bits
* @param x The value which we want to rotate
* @param n The number how many we waht to rotate
* @return A bit rotated number
*/
template <typename T>
static FORCEINLINE T ROL(const T x, const uint8 n)
{
return (T)(x << n | x >> (sizeof(x) * 8 - n));
}
/**
* ROtate x Right by n
*
* @note Assumes a byte has 8 bits
* @param x The value which we want to rotate
* @param n The number how many we waht to rotate
* @return A bit rotated number
*/
template <typename T>
static FORCEINLINE T ROR(const T x, const uint8 n)
{
return (T)(x >> n | x << (sizeof(x) * 8 - n));
}
/**
* Do an operation for each set set bit in a value.
*
* This macros is used to do an operation for each set
* bit in a variable. The first variable can be reused
* in the operation due to it's the bit position counter.
* The second variable will be cleared during the usage
*
* @param i The position counter
* @param b The value which we check for set bits
*/
#define FOR_EACH_SET_BIT(i, b) \
for (i = 0; b != 0; i++, b >>= 1) \
if (b & 1)
#if defined(__APPLE__)
/* Make endian swapping use Apple's macros to increase speed
* (since it will use hardware swapping if available).
* Even though they should return uint16 and uint32, we get
* warnings if we don't cast those (why?) */
#define BSWAP32(x) ((uint32)Endian32_Swap(x))
#define BSWAP16(x) ((uint16)Endian16_Swap(x))
#else
/**
* Perform a 32 bits endianness bitswap on x.
* @param x the variable to bitswap
* @return the bitswapped value.
*/
static FORCEINLINE uint32 BSWAP32(uint32 x)
{
#if defined(__GNUC__) && ((__GNUC__ > 4) || ((__GNUC__ == 4) && __GNUC_MINOR__ >= 3))
/* GCC >= 4.3 provides a builtin, resulting in faster code */
return (uint32)__builtin_bswap32((int32)x);
#else
return ((x >> 24) & 0xFF) | ((x >> 8) & 0xFF00) | ((x << 8) & 0xFF0000) | ((x << 24) & 0xFF000000);
#endif /* defined(__GNUC__) */
}
/**
* Perform a 16 bits endianness bitswap on x.
* @param x the variable to bitswap
* @return the bitswapped value.
*/
static FORCEINLINE uint16 BSWAP16(uint16 x)
{
return (x >> 8) | (x << 8);
}
#endif /* __APPLE__ */
#endif /* BITMATH_FUNC_HPP */
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