[PATCH 1/5] add SWAP macro
- From
René Scharfe <l.s.r@web.de>
- Date
- Jan 28, 2017, 21:38 UTC
- Message-ID
- <0bdb58a6-3a7f-2218-4b70-c591ae90e95e@web.de>
- In-Reply-To
- <8ef4c833-45bd-6831-0683-6d01f30aa518@web.de>
Add a macro for exchanging the values of variables. It allows users to avoid repetition and takes care of the temporary variable for them. It also makes sure that the storage sizes of its two parameters are the same. Its memcpy(1) calls are optimized away by current compilers.
Also add a conservative semantic patch for transforming only swaps of variables of the same type.
Signed-off-by: Rene Scharfe <l.s.r@web.de> --- contrib/coccinelle/swap.cocci | 28 ++++++++++++++++++++++++++++ git-compat-util.h | 10 ++++++++++ 2 files changed, 38 insertions(+) create mode 100644 contrib/coccinelle/swap.cocci
diff --git a/contrib/coccinelle/swap.cocci b/contrib/coccinelle/swap.cocci new file mode 100644 index 0000000000..a0934d1fda --- /dev/null +++ b/contrib/coccinelle/swap.cocci @@ -0,0 +1,28 @@ +@ swap_with_declaration @ +type T; +identifier tmp; +T a, b; +@@ +- T tmp = a; ++ T tmp; ++ tmp = a; + a = b; + b = tmp; + +@ swap @ +type T; +T tmp, a, b; +@@ +- tmp = a; +- a = b; +- b = tmp; ++ SWAP(a, b); + +@ extends swap @ +identifier unused; +@@ + { + ... +- T unused; + ... when != unused + } diff --git a/git-compat-util.h b/git-compat-util.h index 87237b092b..66cd466eea 100644 --- a/git-compat-util.h +++ b/git-compat-util.h @@ -527,6 +527,16 @@ static inline int ends_with(const char *str, const char *suffix) return strip_suffix(str, suffix, &len); } +#define SWAP(a, b) do { \ + void *_swap_a_ptr = &(a); \ + void *_swap_b_ptr = &(b); \ + unsigned char _swap_buffer[sizeof(a)]; \ + memcpy(_swap_buffer, _swap_a_ptr, sizeof(a)); \ + memcpy(_swap_a_ptr, _swap_b_ptr, sizeof(a) + \ + BUILD_ASSERT_OR_ZERO(sizeof(a) == sizeof(b))); \ + memcpy(_swap_b_ptr, _swap_buffer, sizeof(a)); \ +} while (0) + #if defined(NO_MMAP) || defined(USE_WIN32_MMAP) #ifndef PROT_READ
-- 2.11.0