intmath.hh

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#ifndef __BASE_INTMATH_HH__
#define __BASE_INTMATH_HH__
 
#include <cassert>
#include <cstdint>
#include <type_traits>
 
#include "base/logging.hh"
#include "base/types.hh"
 
inline uint64_t
power(uint32_t n, uint32_t e)
{
    uint64_t result = 1;
    uint64_t component = n;
    while (e) {
        uint64_t last = result;
        if (e & 0x1)
            result *= component;
        warn_if(result < last, "power() overflowed!");
        e >>= 1;
        component *= component;
    }
    return result;
}
 
template <class T>
inline typename std::enable_if<std::is_integral<T>::value, int>::type
floorLog2(T x)
{
    assert(x > 0);
 
    // A guaranteed unsigned version of x.
    uint64_t ux = (typename std::make_unsigned<T>::type)x;
 
    int y = 0;
    constexpr auto ts = sizeof(T);
 
    if (ts >= 8 && (ux & ULL(0xffffffff00000000))) { y += 32; ux >>= 32; }
    if (ts >= 4 && (ux & ULL(0x00000000ffff0000))) { y += 16; ux >>= 16; }
    if (ts >= 2 && (ux & ULL(0x000000000000ff00))) { y +=  8; ux >>=  8; }
    if (ux & ULL(0x00000000000000f0)) { y +=  4; ux >>=  4; }
    if (ux & ULL(0x000000000000000c)) { y +=  2; ux >>=  2; }
    if (ux & ULL(0x0000000000000002)) { y +=  1; }
 
    return y;
}
 
template <class T>
inline int
ceilLog2(const T& n)
{
    assert(n > 0);
    if (n == 1)
        return 0;
 
    return floorLog2(n - (T)1) + 1;
}
 
template <class T>
inline bool
isPowerOf2(const T& n)
{
    // If n is non-zero, and subtracting one borrows all the way to the MSB
    // and flips all bits, then this is a power of 2.
    return n && !(n & (n - 1));
}
 
template <class T, class U>
inline T
divCeil(const T& a, const U& b)
{
    return (a + b - 1) / b;
}
 
template <class T, class U>
inline T
roundUp(const T& val, const U& align)
{
    assert(isPowerOf2(align));
    T mask = (T)align - 1;
    return (val + mask) & ~mask;
}
 
template <class T, class U>
inline T
roundDown(const T& val, const U& align)
{
    assert(isPowerOf2(align));
    T mask = (T)align - 1;
    return val & ~mask;
}
 
#endif // __BASE_INTMATH_HH__