Init

cppdraft/ptr/align.md

@@ -0,0 +1,130 @@
+[ptr.align]
+
+# 20 Memory management library [[mem]](./#mem)
+
+## 20.2 Memory [[memory]](memory#ptr.align)
+
+### 20.2.5 Pointer alignment [ptr.align]
+
+[🔗](#lib:align)
+
+`void* align(size_t alignment, size_t size, void*& ptr, size_t& space);
+`
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L946)
+
+*Preconditions*: 
+
+- [(1.1)](#1.1)
+
+alignment is a power of two
+
+- [(1.2)](#1.2)
+
+ptr represents the address of contiguous storage of at leastspace bytes
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L957)
+
+*Effects*: If it is possible to fit size bytes
+of storage aligned by alignment into the buffer pointed to byptr with length space, the function updatesptr to represent the first possible address of such storage
+and decreases space by the number of bytes used for alignment[.](#2.sentence-1)
+
+Otherwise, the function does nothing[.](#2.sentence-2)
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L966)
+
+*Returns*: A null pointer if the requested aligned buffer
+would not fit into the available space, otherwise the adjusted value
+of ptr[.](#3.sentence-1)
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L972)
+
+[*Note [1](#note-1)*:
+
+The function updates its ptr and space arguments so that it can be called repeatedly
+with possibly different alignment and size arguments for the same buffer[.](#4.sentence-1)
+
+— *end note*]
+
+[🔗](#lib:assume_aligned)
+
+`template<size_t N, class T>
+  constexpr T* assume_aligned(T* ptr);
+`
+
+[5](#5)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L988)
+
+*Mandates*: N is a power of two[.](#5.sentence-1)
+
+[6](#6)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L992)
+
+*Preconditions*: ptr points to an object X of
+a type similar ([[conv.qual]](conv.qual "7.3.6 Qualification conversions")) to T,
+where X has alignment N ([[basic.align]](basic.align "6.8.3 Alignment"))[.](#6.sentence-1)
+
+[7](#7)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L998)
+
+*Returns*: ptr[.](#7.sentence-1)
+
+[8](#8)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L1002)
+
+*Throws*: Nothing[.](#8.sentence-1)
+
+[9](#9)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L1006)
+
+[*Note [2](#note-2)*:
+
+The alignment assumption on an object X expressed by a call to assume_aligned might result in generation of more efficient code[.](#9.sentence-1)
+
+It is up to the program to ensure that the assumption actually holds[.](#9.sentence-2)
+
+The call does not cause the implementation to verify or enforce this[.](#9.sentence-3)
+
+An implementation might only make the assumption
+for those operations on X that access X through the pointer returned by assume_aligned[.](#9.sentence-4)
+
+— *end note*]
+
+[🔗](#lib:is_sufficiently_aligned)
+
+`template<size_t Alignment, class T>
+  bool is_sufficiently_aligned(T* ptr);
+`
+
+[10](#10)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L1026)
+
+*Preconditions*: p points to
+an object X of a type similar ([[conv.qual]](conv.qual "7.3.6 Qualification conversions")) to T[.](#10.sentence-1)
+
+[11](#11)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L1031)
+
+*Returns*: true if X has alignment at least Alignment,
+otherwise false[.](#11.sentence-1)
+
+[12](#12)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L1036)
+
+*Throws*: Nothing[.](#12.sentence-1)