~mdw / mLib / blame
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1 | .\" -*-nroff-*- |
| 2 | .\" | |
| 3 | .\" Manual for memory alignment | |
| 4 | .\" | |
| 5 | .\" (c) 2009, 2024 Straylight/Edgeware | |
| 6 | .\" | |
| 7 | . | |
| 8 | .\"----- Licensing notice --------------------------------------------------- | |
| 9 | .\" | |
| 10 | .\" This file is part of the mLib utilities library. | |
| 11 | .\" | |
| 12 | .\" mLib is free software: you can redistribute it and/or modify it under | |
| 13 | .\" the terms of the GNU Library General Public License as published by | |
| 14 | .\" the Free Software Foundation; either version 2 of the License, or (at | |
| 15 | .\" your option) any later version. | |
| 16 | .\" | |
| 17 | .\" mLib is distributed in the hope that it will be useful, but WITHOUT | |
| 18 | .\" ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 19 | .\" FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public | |
| 20 | .\" License for more details. | |
| 21 | .\" | |
| 22 | .\" You should have received a copy of the GNU Library General Public | |
| 23 | .\" License along with mLib. If not, write to the Free Software | |
| 24 | .\" Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, | |
| 25 | .\" USA. | |
| 26 | . | |
| 27 | .\"-------------------------------------------------------------------------- | |
| 28 | .so ../defs.man \" @@@PRE@@@ | |
| 29 | . | |
| 30 | .\"-------------------------------------------------------------------------- | |
| 31 | .TH align 3mLib "4 January 2009" "Straylight/Edgeware" "mLib utilities library" | |
| 32 | .\" @ALIGN | |
| 289651a7 | 33 | .\" @ALIGNOF |
| c4ccbbf9 MW |
34 | . |
| 35 | .\"-------------------------------------------------------------------------- | |
| 36 | .SH NAME | |
| 37 | align \- alignment utilities | |
| 38 | . | |
| 39 | .\"-------------------------------------------------------------------------- | |
| 40 | .SH SYNOPSIS | |
| 41 | . | |
| 42 | .nf | |
| 43 | .B "#include <mLib/align.h>" | |
| 44 | .PP | |
| 289651a7 MW |
45 | .B "union align { ...\& };" |
| 46 | .PP | |
| 47 | .BI "void ALIGN(size_t &" sz ");" | |
| 48 | .BI "size_t ALIGNOF(" type ); | |
| c4ccbbf9 MW |
49 | .fi |
| 50 | . | |
| 51 | .\"-------------------------------------------------------------------------- | |
| 52 | .SH DESCRIPTION | |
| 289651a7 MW |
53 | . |
| 54 | The | |
| 55 | .B "union align" | |
| 56 | type is (a reasonable guess at) a type with the | |
| 57 | implementation's most restrictive alignment requirements; | |
| 58 | i.e., if a pointer is suitably aligned for | |
| 59 | .B "union align" | |
| 60 | value, | |
| 61 | then it should be suitably aligned for any other value too. | |
| 62 | .PP | |
| 63 | The | |
| 64 | .B ALIGNOF | |
| 65 | macro returns the alignment required for the given | |
| 66 | .IR type ; | |
| 67 | i.e., if an address is suitably aligned for a | |
| 68 | .I type | |
| 69 | value if and only if it is a multiple of | |
| 70 | .BR ALIGNOF( type ) \fR. | |
| 71 | .PP | |
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72 | The |
| 73 | .B ALIGN | |
| 289651a7 MW |
74 | macro rounds its argument |
| 75 | .I sz | |
| 76 | up to the next multiple of | |
| 77 | .BR "ALIGNOF(union align)" : | |
| 78 | so, if | |
| 79 | .I sz | |
| 80 | is an offset from the start of a suitably aligned chunk of memory, | |
| 81 | e.g., returned by | |
| 82 | .BR malloc (3), | |
| 83 | then | |
| 84 | .BI ALIGN( sz ) | |
| 85 | adjusts | |
| c4ccbbf9 | 86 | .I sz |
| 289651a7 MW |
87 | in place, including additional padding |
| 88 | so that the new offset is also suitably aligned. | |
| 89 | The intent is to assist with writing fairly portable memory allocators, | |
| 90 | which must return correctly-aligned memory. | |
| c4ccbbf9 MW |
91 | . |
| 92 | .\"-------------------------------------------------------------------------- | |
| 93 | .SH "SEE ALSO" | |
| 94 | . | |
| 95 | .BR mLib (3). | |
| 96 | . | |
| 97 | .\"-------------------------------------------------------------------------- | |
| 98 | .SH "AUTHOR" | |
| 99 | . | |
| 100 | Mark Wooding, <mdw@distorted.org.uk> | |
| 101 | . | |
| 102 | .\"----- That's all, folks -------------------------------------------------- |