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[dragonfly.git] / lib / libc / stdlib / posix_memalign.3
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28.Dd May 2, 2009
29.Dt POSIX_MEMALIGN 3
30.Os
31.Sh NAME
32.Nm posix_memalign
33.Nd aligned memory allocation
34.Sh LIBRARY
35.Lb libc
36.Sh SYNOPSIS
37.In stdlib.h
38.Ft int
39.Fn posix_memalign "void **ptr" "size_t alignment" "size_t size"
40.Sh DESCRIPTION
41The
42.Fn posix_memalign
43function allocates
44.Fa size
45bytes of memory such that the allocation's base address is an even multiple of
46.Fa alignment ,
47and returns the allocation in the value pointed to by
48.Fa ptr .
49.Pp
50The requested
51.Fa alignment
52must be a power of 2 at least as large as
53.Fn sizeof "void *" .
54.Pp
55Memory that is allocated via
56.Fn posix_memalign
57can be used as an argument in subsequent calls to
58.Xr realloc 3 ,
59.Xr reallocf 3 ,
60and
61.Xr free 3 .
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62.Sh IMPLEMENTATION NOTES
63The
64.Fn posix_memalign
65function is directly supported by matching the requested alignment against a zone
66of the slab allocator with a compatible chunking, and using the power-of-2
67shortcut whenever possible.
68Alignments beyond those supported by the zone mechanism are still
69guaranteed using cute
70.Xr mmap 2
71tricks.
72Our
73.Fn posix_memalign
74is thus able to take advantage of the slab allocator to produce
75well-fitted results when the requests are reasonable.
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76.Sh RETURN VALUES
77The
78.Fn posix_memalign
79function returns the value 0 if successful; otherwise it returns an error value.
80.Sh ERRORS
81The
82.Fn posix_memalign
83function will fail if:
84.Bl -tag -width Er
85.It Bq Er EINVAL
86The
87.Fa alignment
88parameter is not a power of 2 at least as large as
89.Fn sizeof "void *" .
90.It Bq Er ENOMEM
91Memory allocation error.
92.El
93.Sh SEE ALSO
94.Xr free 3 ,
95.Xr malloc 3 ,
96.Xr realloc 3 ,
97.Xr reallocf 3 ,
98.Xr valloc 3
99.Sh STANDARDS
100The
101.Fn posix_memalign
102function conforms to
103.St -p1003.1-2008 .