Re: [Libguestfs] [PATCH nbdkit 2/2] common/include/checked-overflow.h: Provide fallback

On Fri, Nov 19, 2021 at 03:35:48PM +0100, Laszlo Ersek wrote: > (1) What is the usual style in nbdkit to highlight parameters of > functions and function-like macros in documentation (comments)? Here I > used parentheses. Normally I use quotes "". We don't have one, so quotes are fine. > (2) In the actual functions, we return "true" for "overflow". My > original conditions expressed "no overflow". In this source code, I > *open-coded* the negations of my original conditions, using De Morgan's > laws. That's because I dislike expressions with an outermost "!" > operator -- whenever I face such an expression, I always work the > outermost negation *into* the formula, as deeply as I can. > > However, I realize the resultant conditions may not be easy to read this > way. Here's an alternative for the body of check_add_overflow(), based > on the original formulation: > > register bool in_range;

> > *r = a + b; > in_range = a <= UINTMAX_MAX - b && *r <= max; > return !in_range; Seems reasonable.

> (3) In the overflow conditions, I used parentheses as sparingly as > possible; only when needed. I could also use as many as possible. > > - Compare, for the addition: > > return ((a > UINTMAX_MAX - b) || (*r > max)); > > or > > in_range = ((a <= UINTMAX_MAX - b) && (*r <= max)); > return !in_range; > > - Compare, for the multiplication: > > return ((b > 0) && ((a > UINTMAX_MAX / b) || (*r > max))); > > or > > in_range = ((b == 0) || ((a <= UINTMAX_MAX / b) && (*r <= max))); > return !in_range; > > What's the preferred form? Personally I use fewest parens, but indicate precedence by dropping whitespace, but I guess whatever works. However you definitely don't need the parens around the entire return value, C doesn't require that.