git.ozlabs.org Git - ccan/blob - ccan/structeq/structeq.h

   1 /* MIT (BSD) license - see LICENSE file for details */
   2 #ifndef CCAN_STRUCTEQ_H
   3 #define CCAN_STRUCTEQ_H
   4 #include <ccan/build_assert/build_assert.h>
   5 #include <ccan/cppmagic/cppmagic.h>
   6 #include <string.h>
   7 #include <stdbool.h>
   8
   9 /**
  10  * STRUCTEQ_DEF - define an ..._eq function to compare two structures.
  11  * @sname: name of the structure, and function (<sname>_eq) to define.
  12  * @padbytes: number of bytes of expected padding, or negative "max".
  13  * @...: name of every member of the structure.
  14  *
  15  * This generates a single memcmp() call in the common case where the
  16  * structure contains no padding.  Since it can't tell the difference between
  17  * padding and a missing member, @padbytes can be used to assert that
  18  * there isn't any, or how many we expect.  A negative number means
  19  * "up to or equal to that amount of padding", as padding can be
  20  * platform dependent.
  21  */
  22 #define STRUCTEQ_DEF(sname, padbytes, ...)                              \
  23 static inline bool CPPMAGIC_GLUE2(sname, _eq)(const struct sname *_a, \
  24                                               const struct sname *_b) \
  25 {                                                                       \
  26         BUILD_ASSERT(((padbytes) < 0 &&                                 \
  27                       CPPMAGIC_JOIN(+, CPPMAGIC_MAP(STRUCTEQ_MEMBER_SIZE_, \
  28                                                     __VA_ARGS__))       \
  29                       - (padbytes) >= sizeof(*_a))                      \
  30                      || CPPMAGIC_JOIN(+, CPPMAGIC_MAP(STRUCTEQ_MEMBER_SIZE_, \
  31                                                       __VA_ARGS__))     \
  32                      + (padbytes) == sizeof(*_a));                      \
  33         if (CPPMAGIC_JOIN(+, CPPMAGIC_MAP(STRUCTEQ_MEMBER_SIZE_, __VA_ARGS__)) \
  34             == sizeof(*_a))                                             \
  35                 return memcmp(_a, _b, sizeof(*_a)) == 0;                \
  36         else                                                            \
  37                 return CPPMAGIC_JOIN(&&,                                \
  38                                      CPPMAGIC_MAP(STRUCTEQ_MEMBER_CMP_, \
  39                                                   __VA_ARGS__));        \
  40 }
  41
  42 /* Helpers */
  43 #define STRUCTEQ_MEMBER_SIZE_(m) sizeof((_a)->m)
  44 #define STRUCTEQ_MEMBER_CMP_(m) memcmp(&_a->m, &_b->m, sizeof(_a->m)) == 0
  45
  46 #endif /* CCAN_STRUCTEQ_H */