SDL_bits.h File Reference

#include <SDL3/SDL_stdinc.h>
#include <SDL3/SDL_begin_code.h>
#include <SDL3/SDL_close_code.h>

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Functions
SDL_FORCE_INLINE int	SDL_MostSignificantBitIndex32 (Uint32 x)
SDL_FORCE_INLINE bool	SDL_HasExactlyOneBitSet32 (Uint32 x)

Function Documentation

SDL_HasExactlyOneBitSet32()

SDL_FORCE_INLINE bool SDL_HasExactlyOneBitSet32

(

Uint32

x

)

Determine if a unsigned 32-bit value has exactly one bit set.

If there are no bits set (x is zero), or more than one bit set, this returns false. If any one bit is exclusively set, this returns true.

Note that this is a forced-inline function in a header, and not a public API function available in the SDL library (which is to say, the code is embedded in the calling program and the linker and dynamic loader will not be able to find this function inside SDL itself).

Parameters

x	the 32-bit value to examine.

Returns

true if exactly one bit is set in x, false otherwise.

\threadsafety It is safe to call this function from any thread.

Since

This function is available since SDL 3.2.0.

Definition at line 132 of file SDL_bits.h.

{
    if (x && !(x & (x - 1))) {
        return true;
    }
    return false;
}

References SDL_FORCE_INLINE.

SDL_MostSignificantBitIndex32()

SDL_FORCE_INLINE int SDL_MostSignificantBitIndex32

(

Uint32

x

)

CategoryBits

Functions for fiddling with bits and bitmasks. Get the index of the most significant (set) bit in a 32-bit number.

This operation can also be stated as "count leading zeroes" and "log base 2".

Note that this is a forced-inline function in a header, and not a public API function available in the SDL library (which is to say, the code is embedded in the calling program and the linker and dynamic loader will not be able to find this function inside SDL itself).

Parameters

x	the 32-bit value to examine.

Returns

the index of the most significant bit, or -1 if the value is 0.

\threadsafety It is safe to call this function from any thread.

Since

This function is available since SDL 3.2.0.

Definition at line 65 of file SDL_bits.h.

{
#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 _SDL_bsr_watcom(x);
#elif defined(_MSC_VER) && _MSC_VER >= 1400
    unsigned long index;
    if (_BitScanReverse(&index, x)) {
        return (int)index;
    }
    return -1;
#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
}

References SDL_FORCE_INLINE.