cmath

cmath.c

/*!
 *  @brief Checks if n is a power of 2.
 *  @returns true if n is power of 2
 */
static inline bool IsPower2(UINT32 n)
{
    return ((n & (n - 1)) == 0);
}

/*!
 *  @brief Computes floor(log2(n))
 *  Works by finding position of MSB set.
 *  @returns -1 if n == 0.
 */
static inline INT32 FloorLog2(UINT32 n)
{
    INT32 p = 0;

    if (n == 0) return -1;

    if (n & 0xffff0000) { p += 16; n >>= 16; }
    if (n & 0x0000ff00)	{ p +=  8; n >>=  8; }
    if (n & 0x000000f0) { p +=  4; n >>=  4; }
    if (n & 0x0000000c) { p +=  2; n >>=  2; }
    if (n & 0x00000002) { p +=  1; }

    return p;
}

/*!
 *  @brief Computes floor(log2(n))
 *  Works by finding position of MSB set.
 *  @returns -1 if n == 0.
 */
static inline INT32 CeilLog2(UINT32 n)
{
    return FloorLog2(n - 1) + 1;
}

1. http://www.stanford.edu/class/cs343/resources/dcache.H
2. http://www.cnblogs.com/xueda120/p/3156283.html
3. http://www.oschina.net/question/129471_39699