util_for_c.h

/*
 * Miscellaneous utilities for C programming language
 */

#ifndef _UTIL_FOR_C_H_
#define _UTIL_FOR_C_H_


#include <stdint.h>


// unions
union union64 {
  uint64_t ui;
  int64_t i;
  double f;
};
union union32 {
  uint32_t ui;
  int32_t i;
  float f;
};
union union16 {
  uint16_t ui;
  int16_t i;
};
union union8 {
  uint8_t ui;
  int8_t i;
};


// A compile time assertion check
#define __paste(foo,bar) (foo##bar)
#define __ct_assert_with_info(predication, info) \
  typedef char __paste(ct_assertion_failed_at_,info)[(predication)?1:-1];
#define __ct_assert(predication) \
  __ct_assert_with_info((predication), __LINE__)


// Obtain the number of elements in the given C array
#define __get_array_len(array) ( sizeof(array) / sizeof((array)[0]) )


// Align the given length to the specified power_of_two
#define __align_to_power_of_two(n_to_align, power_of_two) \
  ( ((n_to_align)+(power_of_two)-1) & ~((power_of_two)-1) )

// Check whether the given length is aligned to the specified power_of_two
#define __is_aligned_to_power_of_two(n_to_test, power_of_two) \
  ( ((n_to_test) & ((power_of_two)-1)) == 0 )


// Obtain the offset of a field in a structure
#define __get_field_offset(struct_name, field_name) \
  ( (uint_fast32_t)(0+&(((struct struct_name*)NULL)->field_name)) )

// Obtain the struct element at the specified offset given the struct ptr
/* #define __get_field_ptr(struct_ptr, offset) \
  ( (void*)(((int8_t*)struct_ptr)+(offset)) ) */


// I've seen this be compiled into one xchg instruction in gcc 4.6.3 Athlon X2
#define __xorswap(p1,p2) *(p1) ^= *(p2); *(p2) ^= *(p1); *(p1) ^= *(p2);

// A quote: "Most modern compilers can optimize the temporary variable in the naive swap,
// in which case the naive swap uses the same amount of memory and the same number of registers
// as the __xorswap does and is at least as fast, and often faster."
#define __swap(p1,p2)\
{\
  __ct_assert( sizeof(*(p2)) == sizeof(*(p1)) )\
  typeof(*(p1)) __tmpvar = *(p1);\
  *(p1) = *(p2);\
  *(p2) = __tmpvar;\
}


// Obtain the absolute value of the given floating point value
inline double _fabsd(double d)
{
  union union64 ret;
  ret.f = d;
  ret.ui &= 0x7fffffffffffffff;
  return ret.f;
}
inline float _fabsf(float f)
{
  union union32 ret;
  ret.f = f;
  ret.ui &= 0x7fffffffu;
  return ret.f;
}


#endif //_UTIL_FOR_C_H_