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Rewrite alignment routines with bitwise operations

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mi_align_{up,down}_ptr are implemented with multiplication and division,
which can be converted to equivalent and deterministic bit operations.
The alignment routines are declared as static inline functions which aid
compiler optimizations.
This commit is contained in:
Jim Huang 2019-07-16 20:09:53 +08:00 • committed by Jim Huang
parent 60e9d3f69d
commit 2a88f7505b
2 changed files with 13 additions and 20 deletions
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14
include/mimalloc-internal.h
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@ -47,7 +47,6 @@ void _mi_os_init(void); // called from process init
void* _mi_os_alloc_aligned(size_t size, size_t alignment, bool commit, mi_os_tld_t* tld);
size_t _mi_os_page_size(void);
uintptr_t _mi_align_up(uintptr_t sz, size_t alignment);
// "segment.c"
mi_page_t* _mi_segment_page_alloc(size_t block_wsize, mi_segments_tld_t* tld, mi_os_tld_t* os_tld);
@ -137,6 +136,19 @@ bool _mi_page_is_valid(mi_page_t* page);
#define MI_INIT128(x) MI_INIT64(x),MI_INIT64(x)
#define MI_INIT256(x) MI_INIT128(x),MI_INIT128(x)
// Return the smallest alignment multiple that is >= sz
static inline uintptr_t _mi_align_up(uintptr_t sz, size_t alignment) {
return ((sz + (alignment - 1)) & (-alignment));
}
static inline void* mi_align_up_ptr(void* p, size_t alignment) {
return (void*)_mi_align_up((uintptr_t)p, alignment);
}
// Return the nearest aligned address at or below p
static inline void* mi_align_down_ptr(void* p, size_t alignment) {
return ((void *)((uintptr_t)p & (-alignment)));
}
// Overflow detecting multiply
#define MI_MUL_NO_OVERFLOW ((size_t)1 << (4*sizeof(size_t))) // sqrt(SIZE_MAX)

19
src/os.c
View file

@ -31,25 +31,6 @@ terms of the MIT license. A copy of the license can be found in the file
----------------------------------------------------------- */
bool _mi_os_decommit(void* addr, size_t size, mi_stats_t* stats);
uintptr_t _mi_align_up(uintptr_t sz, size_t alignment) {
uintptr_t x = (sz / alignment) * alignment;
if (x < sz) x += alignment;
if (x < sz) return 0; // overflow
return x;
}
static void* mi_align_up_ptr(void* p, size_t alignment) {
return (void*)_mi_align_up((uintptr_t)p, alignment);
}
static uintptr_t _mi_align_down(uintptr_t sz, size_t alignment) {
return (sz / alignment) * alignment;
}
static void* mi_align_down_ptr(void* p, size_t alignment) {
return (void*)_mi_align_down((uintptr_t)p, alignment);
}
// page size (initialized properly in `os_init`)
static size_t os_page_size = 4096;