[PATCH 2/2] Replace xrealloc with xreallocarray

[Dmitry V. Levin]

On Thu, Mar 26, 2015 at 02:32:34AM +0900, Masatake YAMATO wrote:
[...]
> +/*
> + * This is sqrt(SIZE_MAX+1), as s1*s2 <= SIZE_MAX
> + * if both s1 < MUL_NO_OVERFLOW and s2 < MUL_NO_OVERFLOW
> + */
> +#define MUL_NO_OVERFLOW	((size_t)1 << (sizeof(size_t) * 4))
> +
> +static void *
> +reallocarray(void *optr, size_t nmemb, size_t size)
>  {
> -	void *r= realloc(ptr, size);
> +	if ((nmemb >= MUL_NO_OVERFLOW || size >= MUL_NO_OVERFLOW) &&
> +	    nmemb > 0 && SIZE_MAX / nmemb < size) {
> +		errno = ENOMEM;
> +		return NULL;
> +	}
> +	return realloc(optr, size * nmemb);
> +}
> +
> +void *
> +xreallocarray(void *optr, size_t nmemb, size_t size)
> +{
> +	void *r;
> +
> +	r = reallocarray(optr, nmemb, size);
>  	if (!r)
>  		die_out_of_memory();
>  	return r;

I don't quite like this implementation.
As the next action in case of integer overflow is die_out_of_memory,
there is no need to optimize for that case.

I think it should rather be something like this:

size_t bytes = nmemb * size;
if ((nmemb | size) >= MUL_NO_OVERFLOW &&
    size && bytes / size != nmemb) {
	die_out_of_memory();
}


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