SDL  2.0
SDL_bits.h File Reference
#include "SDL_stdinc.h"
#include "begin_code.h"
#include "close_code.h"
+ Include dependency graph for SDL_bits.h:

Go to the source code of this file.

Functions

SDL_FORCE_INLINE int SDL_MostSignificantBitIndex32 (Uint32 x)
 
SDL_FORCE_INLINE SDL_bool SDL_HasExactlyOneBitSet32 (Uint32 x)
 

Detailed Description

Functions for fiddling with bits and bitmasks.

Definition in file SDL_bits.h.

Function Documentation

◆ SDL_HasExactlyOneBitSet32()

SDL_FORCE_INLINE SDL_bool SDL_HasExactlyOneBitSet32 ( Uint32  x)

Definition at line 110 of file SDL_bits.h.

111 {
112  if (x && !(x & (x - 1))) {
113  return SDL_TRUE;
114  }
115  return SDL_FALSE;
116 }
@ SDL_TRUE
Definition: SDL_stdinc.h:181
@ SDL_FALSE
Definition: SDL_stdinc.h:180

References SDL_FALSE, and SDL_TRUE.

◆ SDL_MostSignificantBitIndex32()

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

Definition at line 60 of file SDL_bits.h.

61 {
62 #if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
63  /* Count Leading Zeroes builtin in GCC.
64  * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
65  */
66  if (x == 0) {
67  return -1;
68  }
69  return 31 - __builtin_clz(x);
70 #elif defined(__WATCOMC__) && defined(__386__)
71  if (x == 0) {
72  return -1;
73  }
74  return _SDL_bsr_watcom(x);
75 #elif defined(_MSC_VER)
76  unsigned long index;
77  if (_BitScanReverse(&index, x)) {
78  return index;
79  }
80  return -1;
81 #else
82  /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
83  * <seander@cs.stanford.edu>, released in the public domain.
84  * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
85  */
86  const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
87  const int S[] = {1, 2, 4, 8, 16};
88 
89  int msbIndex = 0;
90  int i;
91 
92  if (x == 0) {
93  return -1;
94  }
95 
96  for (i = 4; i >= 0; i--)
97  {
98  if (x & b[i])
99  {
100  x >>= S[i];
101  msbIndex |= S[i];
102  }
103  }
104 
105  return msbIndex;
106 #endif
107 }
uint32_t Uint32
Definition: SDL_stdinc.h:220