blender-legacy/blender-2.79b/source/blender/blenlib/BLI_utildefines_iter.h

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 * modify it under the terms of the GNU General Public License
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#ifndef __BLI_UTILDEFINES_ITER_H__
#define __BLI_UTILDEFINES_ITER_H__

/** \file BLI_utildefines_iter.h
 *  \ingroup bli
 *
 * General looping helpers, use `BLI_FOREACH` prefix.
 */

/**
 * Even value distribution.
 *
 * \a src must be larger than \a dst,
 * \a dst defines the number of iterations, their values are evenly spaced.
 *
 * The following pairs represent (src, dst) arguments and the values they loop over.
 * <pre>
 * (19, 4) ->    [2, 7, 11. 16]
 * (100, 5) ->   [9, 29, 49, 69, 89]
 * (100, 3) ->   [16, 49, 83]
 * (100, 100) -> [0..99]
 * </pre>
 * \note this is mainly useful for numbers that might not divide evenly into eachother.
 */
#define BLI_FOREACH_SPARSE_RANGE(src, dst, i) \
for (int _src = (src), _src2 = _src * 2, _dst2 = (dst) * 2, _error = _dst2 - _src, i = 0, _delta; \
     ((void)(_delta = divide_floor_i(_error, _dst2)), \
      (void)(i -= _delta), \
      (i < _src)); \
     _error -= (_delta * _dst2) + _src2)

#endif  /* __BLI_UTILDEFINES_ITER_H__ */