Make our overflow check look more like gcc/clang's

Make our overflow checking look more like gcc and clang's, so that
we can substitute it out with the compiler instrinsics on platforms
that support it.  This means dropping the ability to pass `NULL` as
an out parameter.

As a result, the macros also get updated to reflect this as well.

1 files changed, 16 insertions, 12 deletions

diff --git a/src/integer.h b/src/integer.h
index a9ed10aae..a4abe2bd1 100644
--- a/src/integer.h
+++ b/src/integer.h
@@ -35,6 +35,13 @@ GIT_INLINE(int) git__is_ulong(git_off_t p)
 	return p == (git_off_t)r;
 }
 
+/** @return true if p fits into the range of an int */
+GIT_INLINE(int) git__is_int(long long p)
+{
+	int r = (int)p;
+	return p == (long long)r;
+}
+
 /**
  * Sets `one + two` into `out`, unless the arithmetic would overflow.
  * @return true if the result fits in a `uint64_t`, false on overflow.
@@ -42,10 +49,9 @@ GIT_INLINE(int) git__is_ulong(git_off_t p)
 GIT_INLINE(bool) git__add_uint64_overflow(uint64_t *out, uint64_t one, uint64_t two)
 {
 	if (UINT64_MAX - one < two)
-		return false;
-	if (out)
-		*out = one + two;
-	return true;
+		return true;
+	*out = one + two;
+	return false;
 }
 
 /**
@@ -55,10 +61,9 @@ GIT_INLINE(bool) git__add_uint64_overflow(uint64_t *out, uint64_t one, uint64_t
 GIT_INLINE(bool) git__add_sizet_overflow(size_t *out, size_t one, size_t two)
 {
 	if (SIZE_MAX - one < two)
-		return false;
-	if (out)
-		*out = one + two;
-	return true;
+		return true;
+	*out = one + two;
+	return false;
 }
 
 /**
@@ -68,10 +73,9 @@ GIT_INLINE(bool) git__add_sizet_overflow(size_t *out, size_t one, size_t two)
 GIT_INLINE(bool) git__multiply_sizet_overflow(size_t *out, size_t one, size_t two)
 {
 	if (one && SIZE_MAX / one < two)
-		return false;
-	if (out)
-		*out = one * two;
-	return true;
+		return true;
+	*out = one * two;
+	return false;
 }
 
 #endif /* INCLUDE_integer_h__ */