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/* nbdkit
* Copyright Red Hat
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* * Neither the name of Red Hat nor the names of its contributors may be
* used to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
* PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#ifndef NBDKIT_ISZERO_H
#define NBDKIT_ISZERO_H
#include <string.h>
#include <stdbool.h>
/* Return true iff the buffer is all zero bytes.
*
* The clever approach here was suggested by Eric Blake. See:
* https://www.redhat.com/archives/libguestfs/2017-April/msg00171.html
* https://rusty.ozlabs.org/?p=560
*
* See also:
* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69908
*/
static inline bool __attribute__ ((__nonnull__ (1)))
is_zero (const char *buffer, size_t size)
{
size_t i;
const size_t limit = size < 16 ? size : 16;
for (i = 0; i < limit; ++i)
if (buffer[i])
return false;
if (size != limit)
return ! memcmp (buffer, buffer + 16, size - 16);
return true;
}
#endif /* NBDKIT_ISZERO_H */
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