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.Dd April 7, 2019
.Dt POSIX_MEMALIGN 3
.Os
.Sh NAME
.Nm posix_memalign ,
.Nm aligned_alloc
.Nd aligned memory allocation
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fn posix_memalign "void **ptr" "size_t alignment" "size_t size"
.Ft void *
.Fn aligned_alloc "size_t alignment" "size_t size"
.Sh DESCRIPTION
The
.Fn posix_memalign
function allocates
.Fa size
bytes of memory such that the allocation's base address is an even multiple of
.Fa alignment ,
and returns the allocation in the value pointed to by
.Fa ptr .
.Pp
The requested
.Fa alignment
must be a power of 2 at least as large as
.Fn sizeof "void *" .
.Pp
Memory that is allocated via
.Fn posix_memalign
can be used as an argument in subsequent calls to
.Xr realloc 3 ,
.Xr reallocf 3 ,
and
.Xr free 3 .
.Pp
The
.Fn aligned_alloc
is similar to
.Fn posix_memalign ,
but it does not have the
.Fn sizeof "void *"
restriction, takes just
.Fa alignment
and
.Fa size
and the allocation pointer is returned.
.Sh IMPLEMENTATION NOTES
The
.Fn posix_memalign
function is directly supported by matching the requested alignment against a zone
of the slab allocator with a compatible chunking, and using the power-of-2
shortcut whenever possible.
Alignments beyond those supported by the zone mechanism are still
guaranteed using cute
.Xr mmap 2
tricks.
Our
.Fn posix_memalign
is thus able to take advantage of the slab allocator to produce
well-fitted results when the requests are reasonable.
.Sh RETURN VALUES
The
.Fn posix_memalign
function returns the value 0 if successful; otherwise it returns an error value.
The
.Fn aligned_alloc
returns a pointer to the allocated memory if successful; otherwise a
.Dv NULL
pointer is returned and
.Va errno
is set.
.Sh ERRORS
The
.Fn posix_memalign
and
.Fn aligned_alloc
functions will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa alignment
parameter is not a power of 2 at least as large as
.Fn sizeof "void *" .
.It Bq Er ENOMEM
Memory allocation error.
.El
.Sh SEE ALSO
.Xr free 3 ,
.Xr malloc 3 ,
.Xr realloc 3 ,
.Xr reallocf 3 ,
.Xr valloc 3
.Sh STANDARDS
The
.Fn posix_memalign
function conforms to
.St -p1003.1-2008 .
The
.Fn aligned_alloc
function conforms to
.St -isoC-2011 .