posix_memalign.3: Uncomment conformance sentence for aligned_alloc().
[dragonfly.git] / lib / libc / stdlib / posix_memalign.3
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cae7f865 28.Dd August 9, 2012
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29.Dt POSIX_MEMALIGN 3
30.Os
31.Sh NAME
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32.Nm posix_memalign ,
33.Nm aligned_alloc
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34.Nd aligned memory allocation
35.Sh LIBRARY
36.Lb libc
37.Sh SYNOPSIS
38.In stdlib.h
39.Ft int
40.Fn posix_memalign "void **ptr" "size_t alignment" "size_t size"
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41.Ft void *
42.Fn aligned_alloc "size_t alignment" "size_t size"
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43.Sh DESCRIPTION
44The
45.Fn posix_memalign
46function allocates
47.Fa size
48bytes of memory such that the allocation's base address is an even multiple of
49.Fa alignment ,
50and returns the allocation in the value pointed to by
51.Fa ptr .
52.Pp
53The requested
54.Fa alignment
55must be a power of 2 at least as large as
56.Fn sizeof "void *" .
57.Pp
58Memory that is allocated via
59.Fn posix_memalign
60can be used as an argument in subsequent calls to
61.Xr realloc 3 ,
62.Xr reallocf 3 ,
63and
64.Xr free 3 .
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65.Pp
66The
67.Fn aligned_alloc
68function is the same as
69.Fn posix_memalign ,
70but it takes just
71.Fa alignment
72and
73.Fa size
74and the allocation pointer is returned.
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75.Sh IMPLEMENTATION NOTES
76The
77.Fn posix_memalign
78function is directly supported by matching the requested alignment against a zone
79of the slab allocator with a compatible chunking, and using the power-of-2
80shortcut whenever possible.
81Alignments beyond those supported by the zone mechanism are still
82guaranteed using cute
83.Xr mmap 2
84tricks.
85Our
86.Fn posix_memalign
87is thus able to take advantage of the slab allocator to produce
88well-fitted results when the requests are reasonable.
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89.Sh RETURN VALUES
90The
91.Fn posix_memalign
92function returns the value 0 if successful; otherwise it returns an error value.
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93The
94.Fn aligned_alloc
95returns a pointer to the allocated memory if successful; otherwise a
96.Dv NULL
97pointer is returned and
98.Va errno
99is set.
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100.Sh ERRORS
101The
102.Fn posix_memalign
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103and
104.Fn aligned_alloc
105functions will fail if:
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106.Bl -tag -width Er
107.It Bq Er EINVAL
108The
109.Fa alignment
110parameter is not a power of 2 at least as large as
111.Fn sizeof "void *" .
112.It Bq Er ENOMEM
113Memory allocation error.
114.El
115.Sh SEE ALSO
116.Xr free 3 ,
117.Xr malloc 3 ,
118.Xr realloc 3 ,
119.Xr reallocf 3 ,
120.Xr valloc 3
121.Sh STANDARDS
122The
123.Fn posix_memalign
124function conforms to
125.St -p1003.1-2008 .
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126The
127.Fn aligned_alloc
128function conforms to
129.St -isoC-2011 .