forked from 0ad/0ad
256 lines
6.0 KiB
C++
256 lines
6.0 KiB
C++
/* Copyright (c) 2010 Wildfire Games
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be included
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* in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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/*
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* bit-twiddling.
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*/
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#ifndef INCLUDED_BITS
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#define INCLUDED_BITS
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/**
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* value of bit number \<n\>.
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*
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* @param n bit index.
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*
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* requirements:
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* - T should be an unsigned type
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* - n must be in [0, CHAR_BIT*sizeof(T)), else the result is undefined!
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**/
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template<typename T>
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inline T Bit(size_t n)
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{
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const T one = T(1);
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return (T)(one << n);
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}
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/**
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* pretty much the same as Bit\<unsigned\>.
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* this is intended for the initialization of enum values, where a
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* compile-time constant is required.
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**/
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#define BIT(n) (1u << (n))
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template<typename T>
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inline bool IsBitSet(T value, size_t index)
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{
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const T bit = Bit<T>(index);
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return (value & bit) != 0;
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}
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// these are declared in the header and inlined to aid compiler optimizations
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// (they can easily end up being time-critical).
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// note: GCC can't inline extern functions, while VC's "Whole Program
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// Optimization" can.
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/**
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* a mask that includes the lowest N bits
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*
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* @param numBits Number of bits in mask.
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**/
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template<typename T>
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inline T bit_mask(size_t numBits)
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{
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const T bitsInT = sizeof(T)*CHAR_BIT;
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const T allBits = (T)~T(0);
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// (shifts of at least bitsInT are undefined)
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if(numBits >= bitsInT)
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return allBits;
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// (note: the previous allBits >> (bitsInT-numBits) is not safe
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// because right-shifts of negative numbers are undefined.)
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const T mask = (T)((T(1) << numBits)-1);
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return mask;
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}
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/**
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* extract the value of bits hi_idx:lo_idx within num
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*
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* example: bits(0x69, 2, 5) == 0x0A
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*
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* @param num number whose bits are to be extracted
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* @param lo_idx bit index of lowest bit to include
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* @param hi_idx bit index of highest bit to include
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* @return value of extracted bits.
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**/
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template<typename T>
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inline T bits(T num, size_t lo_idx, size_t hi_idx)
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{
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const size_t numBits = (hi_idx - lo_idx)+1; // # bits to return
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T result = T(num >> lo_idx);
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result = T(result & bit_mask<T>(numBits));
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return result;
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}
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/**
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* set the value of bits hi_idx:lo_idx
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*
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* @param lo_idx bit index of lowest bit to include
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* @param hi_idx bit index of highest bit to include
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* @param value new value to be assigned to these bits
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**/
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template<typename T>
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inline T SetBitsTo(T num, size_t lo_idx, size_t hi_idx, size_t value)
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{
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const size_t numBits = (hi_idx - lo_idx)+1;
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debug_assert(value < (T(1) << numBits));
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const T mask = bit_mask<T>(numBits) << lo_idx;
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T result = num & ~mask;
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result = T(result | (value << lo_idx));
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return result;
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}
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/**
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* @return number of 1-bits in mask
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**/
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template<typename T>
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inline size_t PopulationCount(T mask)
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{
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// note: a more complex but probably faster method is given at
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// http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
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size_t num1Bits = 0;
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while(mask)
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{
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mask &= mask-1; // clear least significant 1-bit
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num1Bits++;
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}
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return num1Bits;
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}
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/**
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* @return whether the given number is a power of two.
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**/
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template<typename T>
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inline bool is_pow2(T n)
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{
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// 0 would pass the test below but isn't a POT.
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if(n == 0)
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return false;
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return (n & (n-1)) == 0;
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}
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template<typename T>
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inline T LeastSignificantBit(T x)
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{
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const T negX = T(~x + 1); // 2's complement (avoids 'negating unsigned type' warning)
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return x & negX;
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}
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template<typename T>
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inline T ClearLeastSignificantBit(T x)
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{
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return x & (x-1);
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}
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/**
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* ceil(log2(x))
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*
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* @param x (unsigned integer)
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* @return ceiling of the base-2 logarithm (i.e. rounded up) or
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* zero if the input is zero.
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**/
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template<typename T>
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inline size_t ceil_log2(T x)
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{
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T bit = 1;
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size_t log = 0;
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while(bit < x && bit != 0) // must detect overflow
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{
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log++;
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bit *= 2;
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}
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return log;
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}
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/**
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* floor(log2(f))
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* fast, uses the FPU normalization hardware.
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*
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* @param x (float) input; MUST be > 0, else results are undefined.
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* @return floor of the base-2 logarithm (i.e. rounded down).
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**/
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extern int floor_log2(const float x);
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/**
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* round up to next larger power of two.
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**/
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template<typename T>
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inline T round_up_to_pow2(T x)
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{
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return T(1) << ceil_log2(x);
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}
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/**
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* round number up/down to the next given multiple.
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*
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* @param n Number to round.
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* @param multiple Must be a power of two.
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**/
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template<typename T>
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inline T round_up(T n, T multiple)
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{
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debug_assert(is_pow2(multiple));
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const T result = (n + multiple-1) & ~(multiple-1);
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debug_assert(n <= result && result < n+multiple);
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return result;
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}
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template<typename T>
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inline T round_down(T n, T multiple)
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{
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debug_assert(is_pow2(multiple));
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const T result = n & ~(multiple-1);
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debug_assert(result <= n && n < result+multiple);
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return result;
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}
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template<typename T>
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inline bool IsAligned(T t, uintptr_t multiple)
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{
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return ((uintptr_t)t % multiple) == 0;
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}
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template<typename T>
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inline T MaxPowerOfTwoDivisor(T value)
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{
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debug_assert(value != T(0));
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for(size_t log2 = 0; log2 < sizeof(T)*CHAR_BIT; log2++)
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{
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if(IsBitSet(value, log2))
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return T(1) << log2;
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}
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debug_assert(0); // unreachable (!= 0 => there is a set bit)
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return 0;
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}
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#endif // #ifndef INCLUDED_BITS
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