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/* $Id$ */

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/** @file bitmath_func.hpp Functions related to bit mathematics. */

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#ifndef BITMATH_FUNC_HPP

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#define BITMATH_FUNC_HPP

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/**

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 * Fetch n bits from x, started at bit s.

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 *

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 * This function can be used to fetch n bits from the value x. The

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 * s value set the startposition to read. The startposition is

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 * count from the LSB and starts at 0. The result starts at a

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 * LSB, as this isn't just an and-bitmask but also some

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 * bit-shifting operations. GB(0xFF, 2, 1) will so

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 * return 0x01 (0000 0001) instead of

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 * 0x04 (0000 0100).

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 *

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 * @param x The value to read some bits.

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 * @param s The startposition to read some bits.

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 * @param n The number of bits to read.

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 * @return The selected bits, aligned to a LSB.

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 */

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{

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	return (x >> s) & ((1U << n) - 1);

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}

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/** Set n bits from x starting at bit s to d

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 *

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 * This function sets n bits from x which started as bit s to the value of

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 * d. The parameters x, s and n works the same as the parameters of

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 * #GB. The result is saved in x again. Unused bits in the window

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 * provided by n are set to 0 if the value of b isn't "big" enough.

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 * This is not a bug, its a feature.

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 *

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 * @note Parameter x must be a variable as the result is saved there.

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 * @note To avoid unexpecting results the value of b should not use more

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 *       space as the provided space of n bits (log2)

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 * @param x The variable to change some bits

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 * @param s The startposition for the new bits

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 * @param n The size/window for the new bits

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 * @param d The actually new bits to save in the defined position.

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 * @return The new value of x

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 */

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{

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	x &= (T)(~(((1U << n) - 1) << s));

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	x |= (T)(d << s);

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	return x;

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}

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/** Add i to n bits of x starting at bit s.

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 *

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 * This add the value of i on n bits of x starting at bit s. The parameters x,

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 * s, i are similar to #GB besides x must be a variable as the result are

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 * saved there. An overflow does not affect the following bits of the given

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 * bit window and is simply ignored.

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 *

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 * @note Parameter x must be a variable as the result is saved there.

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 * @param x The variable to add some bits at some position

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 * @param s The startposition of the addition

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 * @param n The size/window for the addition

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 * @param i The value to add at the given startposition in the given window.

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 * @return The new value of x

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 */

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{

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	const T mask = (T)(((1U << n) - 1) << s);

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	x = (T)((x & ~mask) | ((x + (i << s)) & mask));

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	return x;

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}

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/**

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 * Checks if a bit in a value is set.

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 *

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 * This function checks if a bit inside a value is set or not.

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 * The y value specific the position of the bit, started at the

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 * LSB and count from 0.

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 *

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 * @param x The value to check

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 * @param y The position of the bit to check, started from the LSB

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 * @return True if the bit is set, false else.

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 */

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{

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	return (x & ((T)1U << y)) != 0;

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}

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/**

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 * Check several bits in a value.

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 *

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 * This macro checks if a value contains at least one bit of an other

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 * value.

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 *

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 * @param x The first value

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 * @param y The second value

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 * @return True if at least one bit is set in both values, false else.

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 */

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#define HASBITS(x, y) (((x) & (y)) != 0)

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/**

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 * Set a bit in a variable.

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 *

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 * This function sets a bit in a variable. The variable is changed

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 * and the value is also returned. Parameter y defines the bit and

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 * starts at the LSB with 0.

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 *

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 * @param x The variable to set a bit

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 * @param y The bit position to set

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 * @return The new value of the old value with the bit set

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 */

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{

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	return x = (T)(x | (T)(1U << y));

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}

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/**

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 * Sets several bits in a variable.

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 *

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 * This macro sets several bits in a variable. The bits to set are provided

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 * by a value. The new value is also returned.

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 *

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 * @param x The variable to set some bits

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 * @param y The value with set bits for setting them in the variable

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 * @return The new value of x

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 */

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#define SETBITS(x, y) ((x) |= (y))

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/**

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 * Clears a bit in a variable.

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 *

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 * This function clears a bit in a variable. The variable is

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 * changed and the value is also returned. Parameter y defines the bit

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 * to clear and starts at the LSB with 0.

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 *

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 * @param x The variable to clear the bit

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 * @param y The bit position to clear

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 * @return The new value of the old value with the bit cleared

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 */

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{

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	return x = (T)(x & ~((T)1U << y));

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}

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/**

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 * Clears several bits in a variable.

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 *

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 * This macro clears several bits in a variable. The bits to clear are

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 * provided by a value. The new value is also returned.

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 *

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 * @param x The variable to clear some bits

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 * @param y The value with set bits for clearing them in the variable

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 * @return The new value of x

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 */

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#define CLRBITS(x, y) ((x) &= ~(y))

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/**

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 * Toggles a bit in a variable.

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 *

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 * This function toggles a bit in a variable. The variable is

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 * changed and the value is also returned. Parameter y defines the bit

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 * to toggle and starts at the LSB with 0.

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 *

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 * @param x The varliable to toggle the bit

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 * @param y The bit position to toggle

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 * @return The new value of the old value with the bit toggled

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 */

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{

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	return x = (T)(x ^ (T)(1U << y));

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}

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/** Lookup table to check which bit is set in a 6 bit variable */

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extern const uint8 _ffb_64[64];

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/**

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 * Returns the first occure of a bit in a 6-bit value (from right).

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 *

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 * Returns the position of the first bit that is not zero, counted from the

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 * LSB. Ie, 110100 returns 2, 000001 returns 0, etc. When x == 0 returns

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 * 0.

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 *

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 * @param x The 6-bit value to check the first zero-bit

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 * @return The first position of a bit started from the LSB or 0 if x is 0.

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 */

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#define FIND_FIRST_BIT(x) _ffb_64[(x)]

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/**

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 * Finds the position of the first bit in an integer.

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 *

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 * This function returns the position of the first bit set in the

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 * integer. It does only check the bits of the bitmask

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 * 0x3F3F (0011111100111111) and checks only the

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 * bits of the bitmask 0x3F00 if and only if the

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 * lower part 0x00FF is 0. This results the bits at 0x00C0 must

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 * be also zero to check the bits at 0x3F00.

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 *

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 * @param value The value to check the first bits

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 * @return The position of the first bit which is set

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 * @see FIND_FIRST_BIT

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 */

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{

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	if ((value & 0xFF) == 0) {

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		return FIND_FIRST_BIT((value >> 8) & 0x3F) + 8;

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	} else {

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		return FIND_FIRST_BIT(value & 0x3F);

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	}

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}

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uint8 FindFirstBit(uint32 x);

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uint8 FindLastBit(uint64 x);

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/**

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 * Clear the first bit in an integer.

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 *

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 * This function returns a value where the first bit (from LSB)

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 * is cleared.

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 * So, 110100 returns 110000, 000001 returns 000000, etc.

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 *

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 * @param value The value to clear the first bit

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 * @return The new value with the first bit cleared

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 */

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{

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	return value &= (T)(value - 1);

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}

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/**

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 * Counts the number of set bits in a variable.

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 *

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 * @param value the value to count the number of bits in.

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 * @return the number of bits.

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 */

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{

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	uint num;

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	/* This loop is only called once for every bit set by clearing the lowest

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	 * bit in each loop. The number of bits is therefore equal to the number of

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	 * times the loop was called. It was found at the following website:

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	 * http://graphics.stanford.edu/~seander/bithacks.html */

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	for (num = 0; value != 0; num++) {

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		value &= (T)(value - 1);

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	}

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	return num;

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}

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/**

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 * ROtate x Left by n

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 *

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 * @note Assumes a byte has 8 bits

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 * @param x The value which we want to rotate

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 * @param n The number how many we waht to rotate

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 * @return A bit rotated number

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 */

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{

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	return (T)(x << n | x >> (sizeof(x) * 8 - n));

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}

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/**

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 * ROtate x Right by n

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 *

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 * @note Assumes a byte has 8 bits

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 * @param x The value which we want to rotate

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 * @param n The number how many we waht to rotate

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 * @return A bit rotated number

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 */

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{

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	return (T)(x >> n | x << (sizeof(x) * 8 - n));

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}

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/**

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 * Do an operation for each set set bit in a value.

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 *

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 * This macros is used to do an operation for each set

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 * bit in a variable. The first variable can be reused

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 * in the operation due to it's the bit position counter.

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 * The second variable will be cleared during the usage

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 *

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 * @param i The position counter

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 * @param b The value which we check for set bits

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 */

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#define FOR_EACH_SET_BIT(i, b)      \

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	for (i = 0; b != 0; i++, b >>= 1) \

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		if (b & 1)

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#if defined(__APPLE__)

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	/* Make endian swapping use Apple's macros to increase speed

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	 * (since it will use hardware swapping if available).

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	 * Even though they should return uint16 and uint32, we get

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	 * warnings if we don't cast those (why?) */

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	#define BSWAP32(x) ((uint32)Endian32_Swap(x))

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	#define BSWAP16(x) ((uint16)Endian16_Swap(x))

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#else

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	/**

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	 * Perform a 32 bits endianness bitswap on x.

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	 * @param x the variable to bitswap

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	 * @return the bitswapped value.

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	 */

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	{

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		return ((x >> 24) & 0xFF) | ((x >> 8) & 0xFF00) | ((x << 8) & 0xFF0000) | ((x << 24) & 0xFF000000);

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	}

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	/**

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	 * Perform a 16 bits endianness bitswap on x.

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	 * @param x the variable to bitswap

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	 * @return the bitswapped value.

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	 */

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	{

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		return (x >> 8) | (x << 8);

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	}

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#endif /* __APPLE__ */

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#endif /* BITMATH_FUNC_HPP */