Skip to content

Add/multiply with overflow tweaks #4945

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
ethomson merged 5 commits into from
Jan 20, 2019
Merged

Add/multiply with overflow tweaks #4945

Changes from 1 commit
Commits
Show all changes
5 commits
Select commit Hold shift + click to select a range
2848923
Let GCC use the add/mul overflow intrinsics
lhchavez Jan 9, 2019
f04f1c7
add with overflow intrinsics: simplify tests
ethomson Jan 20, 2019
c6d47ac
Remove unused git__add_uint64_overflow
ethomson Jan 20, 2019
abbc07f
add with overflow: use SizeTAdd on Windows
ethomson Jan 20, 2019
75444d9
add with overflow: correct documentation
ethomson Jan 20, 2019
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
Next Next commit
Let GCC use the add/mul overflow intrinsics 
This change tweaks the macros for git__{add,multiply}_sizet_overflow so
that GCC can use them.

It also stops using the uadd,umul versions since the add,mul can handle
way more cases.
  • Loading branch information
@lhchavez
lhchavez committed Jan 10, 2019
commit 2848923a2f5099b6d105b0b30212134d84377dee
40 changes: 30 additions & 10 deletions src/integer.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -55,16 +55,36 @@ GIT_INLINE(bool) git__add_uint64_overflow(uint64_t *out, uint64_t one, uint64_t
}

/* Use clang/gcc compiler intrinsics whenever possible */
#if (SIZE_MAX == ULONG_MAX) && __has_builtin(__builtin_uaddl_overflow)
# define git__add_sizet_overflow(out, one, two) \
__builtin_uaddl_overflow(one, two, out)
# define git__multiply_sizet_overflow(out, one, two) \
__builtin_umull_overflow(one, two, out)
#elif (SIZE_MAX == UINT_MAX) && __has_builtin(__builtin_uadd_overflow)
# define git__add_sizet_overflow(out, one, two) \
__builtin_uadd_overflow(one, two, out)
# define git__multiply_sizet_overflow(out, one, two) \
__builtin_umul_overflow(one, two, out)
#if (__has_builtin(__builtin_add_overflow) || \
(defined(__GNUC__) && (__GNUC__ >= 5)))

/*
* Even though __builtin_{add,mul}_overflow should be able to handle all
* possible cases (since it can accept any type), under some configurations
* clang would need a dependency on compiler-rt. In order to avoid that, we
* attempt to choose one of the explicit unsigned long long / unsigned long
* versions of the intrinsics if possible. Unfortunately, unsigned long long
* and unsigned long are still different types to the compiler, so we need to
* still do some additional sniffing to prevent MinGW 64 from choosing the
* wrong version and triggering compiler warnings.
*/
# if (SIZE_MAX == ULLONG_MAX) && (ULONG_MAX == ULLONG_MAX) && defined(_WIN64)
# define git__add_sizet_overflow(out, one, two) \
__builtin_uaddll_overflow(one, two, out)
# define git__multiply_sizet_overflow(out, one, two) \
__builtin_umulll_overflow(one, two, out)
# elif (SIZE_MAX == ULONG_MAX) && (ULONG_MAX == ULLONG_MAX)
# define git__add_sizet_overflow(out, one, two) \
__builtin_uaddl_overflow(one, two, out)
# define git__multiply_sizet_overflow(out, one, two) \
__builtin_umull_overflow(one, two, out)
# else
# define git__add_sizet_overflow(out, one, two) \
__builtin_add_overflow(one, two, out)
# define git__multiply_sizet_overflow(out, one, two) \
__builtin_mul_overflow(one, two, out)
# endif

#else

/**
Expand Down