#include "SDL_stdinc.h"
#include "begin_code.h"
#include "close_code.h"

Include dependency graph for SDL_bits.h:

This graph shows which files directly or indirectly include this file:

Functions
SDL_FORCE_INLINE int	SDL_MostSignificantBitIndex32 (Uint32 x)

Detailed Description

Functions for fiddling with bits and bitmasks.

Definition in file SDL_bits.h.

Function Documentation

SDL_FORCE_INLINE int SDL_MostSignificantBitIndex32 ( Uint32 x )

Get the index of the most significant bit. Result is undefined when called with 0. This operation can also be stated as "count leading zeroes" and "log base 2".

Returns: Index of the most significant bit, or -1 if the value is 0.

Definition at line 61 of file SDL_bits.h.

References i.

Referenced by SDL_PrivateShouldInitSubsystem(), SDL_PrivateShouldQuitSubsystem(), SDL_PrivateSubsystemRefCountDecr(), SDL_PrivateSubsystemRefCountIncr(), and SDL_WasInit().

{
#if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
    /* Count Leading Zeroes builtin in GCC.
     * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
     */
    if (x == 0) {
        return -1;
    }
    return 31 - __builtin_clz(x);
#elif defined(__WATCOMC__) && defined(__386__)
    if (x == 0) {
        return -1;
    }
    return 31 - _SDL_clz_watcom(x);
#else
    /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
     * <seander@cs.stanford.edu>, released in the public domain.
     * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
     */
    const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
    const int    S[] = {1, 2, 4, 8, 16};
    int msbIndex = 0;
    int i;
    if (x == 0) {
        return -1;
    }
    for (i = 4; i >= 0; i--)
    {
        if (x & b[i])
        {
            x >>= S[i];
            msbIndex |= S[i];
        }
    }
    return msbIndex;
#endif
}