Re: [PATCH] ALSA: Remove subsystem-specific malloc (1/8)

[dean gaudet]

On Wed, 9 Jun 2004, Pekka Enberg wrote:

> +void *kcalloc(size_t n, size_t size, int flags)
> +{
> +	if (n != 0 && size > INT_MAX / n)
> +		return NULL;

division isn't very efficient :)  it's typically a 40+ cycle operation.

there's almost certainly more efficient ways to do this with per-target
assembly... but you should probably just crib the code from glibc which
avoids division for small allocations:

  /* size_t is unsigned so the behavior on overflow is defined.  */
  bytes = n * elem_size;
#define HALF_INTERNAL_SIZE_T \
  (((INTERNAL_SIZE_T) 1) << (8 * sizeof (INTERNAL_SIZE_T) / 2))
  if (__builtin_expect ((n | elem_size) >= HALF_INTERNAL_SIZE_T, 0)) {
    if (elem_size != 0 && bytes / elem_size != n) {
      MALLOC_FAILURE_ACTION;
      return 0;
    }
  }

-dean
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/