From: Jonathan Nieder <jrnieder@gmail.com>
To: Erik Faye-Lund <kusmabite@gmail.com>
Cc: git@vger.kernel.org
Subject: Re: [PATCH] do not depend on undefined signed integer overflow
Date: Mon, 4 Oct 2010 15:48:48 -0500 [thread overview]
Message-ID: <20101004204848.GI6466@burratino> (raw)
In-Reply-To: <1286221388-4908-1-git-send-email-kusmabite@gmail.com>
Erik Faye-Lund wrote:
> --- a/git-compat-util.h
> +++ b/git-compat-util.h
> @@ -28,6 +28,15 @@
> #define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0]))
> #define bitsizeof(x) (CHAR_BIT * sizeof(x))
>
> +/*
> + * Signed integer overflow is undefined in C and some compilers take
> + * advantage of this when optimizing
[...]
> + */
> +#define signed_add_overflows(a, b) \
> + ((b) > ((INTMAX_MAX >> (bitsizeof(uintmax_t) - bitsizeof(a))) - (a)))
Clever. I like it.
prev parent reply other threads:[~2010-10-04 20:52 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-04 19:43 [PATCH] do not depend on undefined signed integer overflow Erik Faye-Lund
2010-10-04 19:47 ` Erik Faye-Lund
2010-10-04 20:48 ` Jonathan Nieder [this message]
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