Import unmodified NetBSD libc in trunk
This patch imports the unmodified current version of NetBSD libc. The NetBSD includes are in /nbsd_include, while the libc code itself is split between lib/nbsd_libc and common/lib/libc.
This commit is contained in:
Gianluca Guida
229
lib/nbsd_libc/stdlib/malloc.3
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229
lib/nbsd_libc/stdlib/malloc.3
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.\" $NetBSD: malloc.3,v 1.38 2010/05/03 08:23:20 jruoho Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the American National Standards Committee X3, on Information
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.\" Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)malloc.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD: src/lib/libc/stdlib/malloc.3,v 1.73 2007/06/15 22:32:33 jasone Exp $
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.\"
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.Dd May 3, 2010
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.Dt MALLOC 3
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.Os
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.Sh NAME
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.Nm malloc , calloc , realloc , free
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.Nd general purpose memory allocation functions
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdlib.h
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.Ft void *
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.Fn malloc "size_t size"
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.Ft void *
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.Fn calloc "size_t number" "size_t size"
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.Ft void *
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.Fn realloc "void *ptr" "size_t size"
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.Ft void
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.Fn free "void *ptr"
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.Sh DESCRIPTION
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The
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.Fn malloc
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function allocates
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.Fa size
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bytes of uninitialized memory.
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The allocated space is suitably aligned (after possible pointer coercion)
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for storage of any type of object.
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.Pp
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The
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.Fn calloc
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function allocates space for
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.Fa number
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objects,
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each
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.Fa size
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bytes in length.
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The result is identical to calling
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.Fn malloc
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with an argument of
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.Dq "number * size" ,
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with the exception that the allocated memory is explicitly initialized
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to zero bytes.
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.Pp
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The
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.Fn realloc
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function changes the size of the previously allocated memory referenced by
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.Fa ptr
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to
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.Fa size
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bytes.
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The contents of the memory are unchanged up to the lesser of the new and
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old sizes.
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If the new size is larger,
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the value of the newly allocated portion of the memory is undefined.
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Upon success, the memory referenced by
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.Fa ptr
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is freed and a pointer to the newly allocated memory is returned.
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Note that
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.Fn realloc
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may move the memory allocation, resulting in a different return value than
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.Fa ptr .
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If
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.Fa ptr
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is
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.Dv NULL ,
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the
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.Fn realloc
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function behaves identically to
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.Fn malloc
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for the specified size.
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.Pp
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The
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.Fn free
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function causes the allocated memory referenced by
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.Fa ptr
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to be made available for future allocations.
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If
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.Fa ptr
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is
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.Dv NULL ,
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no action occurs.
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.Sh RETURN VALUES
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The
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.Fn malloc
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and
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.Fn calloc
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functions return a pointer to the allocated memory if successful; otherwise
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a
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.Dv NULL
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pointer is returned and
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.Va errno
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is set to
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.Er ENOMEM .
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.Pp
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The
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.Fn realloc
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function returns a pointer, possibly identical to
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.Fa ptr ,
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to the allocated memory
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if successful; otherwise a
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.Dv NULL
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pointer is returned, and
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.Va errno
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is set to
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.Er ENOMEM
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if the error was the result of an allocation failure.
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The
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.Fn realloc
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function always leaves the original buffer intact
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when an error occurs.
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.Pp
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The
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.Fn free
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function returns no value.
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.Sh EXAMPLES
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When using
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.Fn malloc ,
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be careful to avoid the following idiom:
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.Bd -literal -offset indent
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if ((p = malloc(number * size)) == NULL)
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err(EXIT_FAILURE, "malloc");
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.Ed
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.Pp
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The multiplication may lead to an integer overflow.
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To avoid this,
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.Fn calloc
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is recommended.
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.Pp
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If
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.Fn malloc
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must be used, be sure to test for overflow:
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.Bd -literal -offset indent
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if (size && number > SIZE_MAX / size) {
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errno = EOVERFLOW;
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err(EXIT_FAILURE, "allocation");
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}
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.Ed
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.Pp
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When using
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.Fn realloc ,
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one must be careful to avoid the following idiom:
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.Pp
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.Bd -literal -offset indent
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nsize += 50;
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if ((p = realloc(p, nsize)) == NULL)
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return NULL;
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.Ed
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.Pp
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Do not adjust the variable describing how much memory has been allocated
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until it is known that the allocation has been successful.
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This can cause aberrant program behavior if the incorrect size value is used.
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In most cases, the above example will also leak memory.
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As stated earlier, a return value of
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.Dv NULL
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indicates that the old object still remains allocated.
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Better code looks like this:
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.Bd -literal -offset indent
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newsize = size + 50;
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if ((p2 = realloc(p, newsize)) == NULL) {
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if (p != NULL)
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free(p);
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p = NULL;
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return NULL;
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}
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p = p2;
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size = newsize;
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.Ed
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.Sh SEE ALSO
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.\" .Xr limits 1 ,
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.Xr madvise 2 ,
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.Xr mmap 2 ,
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.Xr sbrk 2 ,
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.Xr alloca 3 ,
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.Xr atexit 3 ,
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.Xr getpagesize 3 ,
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.Xr memory 3 ,
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.Xr posix_memalign 3
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.Pp
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For the implementation details, see
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.Xr jemalloc 3 .
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.Sh STANDARDS
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The
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.Fn malloc ,
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.Fn calloc ,
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.Fn realloc
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and
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.Fn free
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functions conform to
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.St -isoC .
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