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-rw-r--r--include/intprops.h18
1 files changed, 14 insertions, 4 deletions
diff --git a/include/intprops.h b/include/intprops.h
index 2b6e5e9..3fe64e8 100644
--- a/include/intprops.h
+++ b/include/intprops.h
@@ -132,7 +132,8 @@
operators might not yield numerically correct answers due to
arithmetic overflow. They do not rely on undefined or
implementation-defined behavior. Their implementations are simple
- and straightforward, but they are a bit harder to use than the
+ and straightforward, but they are harder to use and may be less
+ efficient than the INT_<op>_WRAPV, INT_<op>_OK, and
INT_<op>_OVERFLOW macros described below.
Example usage:
@@ -157,6 +158,9 @@
must have minimum value MIN and maximum MAX. Unsigned types should
use a zero MIN of the proper type.
+ Because all arguments are subject to integer promotions, these
+ macros typically do not work on types narrower than 'int'.
+
These macros are tuned for constant MIN and MAX. For commutative
operations such as A + B, they are also tuned for constant B. */
@@ -338,9 +342,15 @@
arguments should not have side effects.
The WRAPV macros are not constant expressions. They support only
- +, binary -, and *. Because the WRAPV macros convert the result,
- they report overflow in different circumstances than the OVERFLOW
- macros do.
+ +, binary -, and *.
+
+ Because the WRAPV macros convert the result, they report overflow
+ in different circumstances than the OVERFLOW macros do. For
+ example, in the typical case with 16-bit 'short' and 32-bit 'int',
+ if A, B and R are all of type 'short' then INT_ADD_OVERFLOW (A, B)
+ returns false because the addition cannot overflow after A and B
+ are converted to 'int', whereas INT_ADD_WRAPV (A, B, &R) returns
+ true or false depending on whether the sum fits into 'short'.
These macros are tuned for their last input argument being a constant.