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Reduced allocation header for strings from 8/16 to 4 bytes

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git-svn-id: http://pugixml.googlecode.com/svn/trunk@653 99668b35-9821-0410-8761-19e4c4f06640
This commit is contained in:
arseny.kapoulkine 2010-08-29 15:18:22 +00:00
parent 40e6900b0f
commit 9ec7db4c0c
1 changed files with 21 additions and 9 deletions
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30
src/pugixml.cpp
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@ -277,8 +277,8 @@ namespace pugi
struct xml_memory_string_header struct xml_memory_string_header
{ {
xml_memory_page* page; uint16_t page_offset; // offset from page->data
size_t full_size; uint16_t full_size; // 0 if string occupies whole page
}; };
struct xml_allocator struct xml_allocator
@ -364,11 +364,11 @@ namespace pugi
char_t* allocate_string(size_t length) char_t* allocate_string(size_t length)
{ {
// get actual size, rounded up to pointer alignment boundary
size_t size = ((length * sizeof(char_t)) + (sizeof(void*) - 1)) & ~(sizeof(void*) - 1);
// allocate memory for string and header block // allocate memory for string and header block
size_t full_size = sizeof(xml_memory_string_header) + size; size_t size = sizeof(xml_memory_string_header) + length * sizeof(char_t);
// round size up to pointer alignment boundary
size_t full_size = (size + (sizeof(void*) - 1)) & ~(sizeof(void*) - 1);
xml_memory_page* page; xml_memory_page* page;
xml_memory_string_header* header = static_cast<xml_memory_string_header*>(allocate_memory(full_size, page)); xml_memory_string_header* header = static_cast<xml_memory_string_header*>(allocate_memory(full_size, page));
@ -376,8 +376,14 @@ namespace pugi
if (!header) return 0; if (!header) return 0;
// setup header // setup header
header->page = page; ptrdiff_t page_offset = reinterpret_cast<char*>(header) - page->data;
header->full_size = full_size;
assert(page_offset >= 0 && page_offset < (1 << 16));
header->page_offset = static_cast<uint16_t>(page_offset);
// full_size == 0 for large strings that occupy the whole page
assert(full_size < (1 << 16) || (page->busy_size == full_size && page_offset == 0));
header->full_size = full_size < (1 << 16) ? static_cast<uint16_t>(full_size) : 0;
return reinterpret_cast<char_t*>(header + 1); return reinterpret_cast<char_t*>(header + 1);
} }
@ -388,7 +394,13 @@ namespace pugi
xml_memory_string_header* header = reinterpret_cast<xml_memory_string_header*>(string) - 1; xml_memory_string_header* header = reinterpret_cast<xml_memory_string_header*>(string) - 1;
// deallocate // deallocate
deallocate_memory(header, header->full_size, header->page); size_t page_offset = offsetof(xml_memory_page, data) + header->page_offset;
xml_memory_page* page = reinterpret_cast<xml_memory_page*>(reinterpret_cast<char*>(header) - page_offset);
// if full_size == 0 then this string occupies the whole page
size_t full_size = header->full_size == 0 ? page->busy_size : header->full_size;
deallocate_memory(header, full_size, page);
} }
xml_memory_page* _root; xml_memory_page* _root;