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      1 /*	$NetBSD: overflow.h,v 1.2 2021/12/19 12:20:53 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2018 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Taylor R. Campbell.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #ifndef _LINUX_OVERFLOW_H_
     33 #define _LINUX_OVERFLOW_H_
     34 
     35 #include <sys/types.h>
     36 
     37 #include <lib/libkern/libkern.h>	/* offsetof */
     38 
     39 #define	check_mul_overflow(a, b, res)	__builtin_mul_overflow(a, b, res)
     40 #define	check_add_overflow(a, b, res)	__builtin_add_overflow(a, b, res)
     41 
     42 /* return x*y saturated at SIZE_MAX */
     43 static inline size_t
     44 array_size(size_t x, size_t y)
     45 {
     46 	size_t xy;
     47 
     48 	if (check_mul_overflow(x, y, &xy))
     49 		return SIZE_MAX;
     50 	return xy;
     51 }
     52 
     53 /* return x*y*z saturated at SIZE_MAX */
     54 static inline size_t
     55 array3_size(size_t x, size_t y, size_t z)
     56 {
     57 	size_t xy, xyz;
     58 
     59 	if (check_mul_overflow(x, y, &xy))
     60 		return SIZE_MAX;
     61 	if (check_mul_overflow(xy, z, &xyz))
     62 		return SIZE_MAX;
     63 	return xyz;
     64 }
     65 
     66 /* return basesize + elemsize*nelem saturated at SIZE_MAX */
     67 static inline size_t
     68 __struct_size(size_t basesize, size_t elemsize, size_t nelem)
     69 {
     70 	size_t arraysize, totalsize;
     71 
     72 	KASSERT(elemsize);
     73 	if ((arraysize = array_size(elemsize, nelem)) == SIZE_MAX)
     74 		return SIZE_MAX;
     75 	if (check_add_overflow(basesize, arraysize, &totalsize))
     76 		return SIZE_MAX;
     77 	return totalsize;
     78 }
     79 
     80 #define	struct_size(p, member, n)					      \
     81 ({									      \
     82 	CTASSERT(sizeof(*(p)) >= offsetof(__typeof__(*(p)), member));	      \
     83 	__struct_size(sizeof(*(p)), sizeof((p)->member[0]), (n));	      \
     84 })
     85 
     86 #endif  /* _LINUX_OVERFLOW_H_ */
     87