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package mem_virtual
import "core:mem"
import "core:intrinsics"
import "core:runtime"
_ :: runtime
DEFAULT_PAGE_SIZE := uint(4096)
Allocator_Error :: mem.Allocator_Error
@(require_results)
reserve :: proc "contextless" (size: uint) -> (data: []byte, err: Allocator_Error) {
return _reserve(size)
}
commit :: proc "contextless" (data: rawptr, size: uint) -> Allocator_Error {
return _commit(data, size)
}
@(require_results)
reserve_and_commit :: proc "contextless" (size: uint) -> (data: []byte, err: Allocator_Error) {
data = reserve(size) or_return
commit(raw_data(data), size) or_return
return
}
decommit :: proc "contextless" (data: rawptr, size: uint) {
_decommit(data, size)
}
release :: proc "contextless" (data: rawptr, size: uint) {
_release(data, size)
}
Protect_Flag :: enum u32 {
Read,
Write,
Execute,
}
Protect_Flags :: distinct bit_set[Protect_Flag; u32]
Protect_No_Access :: Protect_Flags{}
protect :: proc "contextless" (data: rawptr, size: uint, flags: Protect_Flags) -> bool {
return _protect(data, size, flags)
}
Memory_Block :: struct {
prev: ^Memory_Block,
base: [^]byte,
used: uint,
committed: uint,
reserved: uint,
}
Memory_Block_Flag :: enum u32 {
Overflow_Protection,
}
Memory_Block_Flags :: distinct bit_set[Memory_Block_Flag; u32]
@(private="file", require_results)
align_formula :: #force_inline proc "contextless" (size, align: uint) -> uint {
result := size + align-1
return result - result%align
}
@(require_results)
memory_block_alloc :: proc(committed, reserved: uint, alignment: uint = 0, flags: Memory_Block_Flags = {}) -> (block: ^Memory_Block, err: Allocator_Error) {
page_size := DEFAULT_PAGE_SIZE
assert(mem.is_power_of_two(uintptr(page_size)))
committed := committed
reserved := reserved
committed = align_formula(committed, page_size)
reserved = align_formula(reserved, page_size)
committed = clamp(committed, 0, reserved)
total_size := uint(reserved + max(alignment, size_of(Platform_Memory_Block)))
base_offset := uintptr(max(alignment, size_of(Platform_Memory_Block)))
protect_offset := uintptr(0)
do_protection := false
if .Overflow_Protection in flags { // overflow protection
rounded_size := reserved
total_size = uint(rounded_size + 2*page_size)
base_offset = uintptr(page_size + rounded_size - uint(reserved))
protect_offset = uintptr(page_size + rounded_size)
do_protection = true
}
pmblock := platform_memory_alloc(0, total_size) or_return
pmblock.block.base = ([^]byte)(pmblock)[base_offset:]
platform_memory_commit(pmblock, uint(base_offset) + committed) or_return
// Should be zeroed
assert(pmblock.block.used == 0)
assert(pmblock.block.prev == nil)
if do_protection {
protect(([^]byte)(pmblock)[protect_offset:], page_size, Protect_No_Access)
}
pmblock.block.committed = committed
pmblock.block.reserved = reserved
return &pmblock.block, nil
}
@(require_results)
alloc_from_memory_block :: proc(block: ^Memory_Block, min_size, alignment: uint) -> (data: []byte, err: Allocator_Error) {
calc_alignment_offset :: proc "contextless" (block: ^Memory_Block, alignment: uintptr) -> uint {
alignment_offset := uint(0)
ptr := uintptr(block.base[block.used:])
mask := alignment-1
if ptr & mask != 0 {
alignment_offset = uint(alignment - (ptr & mask))
}
return alignment_offset
}
do_commit_if_necessary :: proc(block: ^Memory_Block, size: uint) -> (err: Allocator_Error) {
if block.committed - block.used < size {
pmblock := (^Platform_Memory_Block)(block)
base_offset := uint(uintptr(pmblock.block.base) - uintptr(pmblock))
// NOTE(bill): [Heuristic] grow the commit size larger than needed
// TODO(bill): determine a better heuristic for this behaviour
extra_size := max(size, block.committed>>1)
platform_total_commit := base_offset + block.used + extra_size
platform_total_commit = align_formula(platform_total_commit, DEFAULT_PAGE_SIZE)
platform_total_commit = min(platform_total_commit, pmblock.reserved)
assert(pmblock.committed <= pmblock.reserved)
assert(pmblock.committed < platform_total_commit)
platform_memory_commit(pmblock, platform_total_commit) or_return
pmblock.committed = platform_total_commit
block.committed = pmblock.committed - base_offset
}
return
}
if block == nil {
return nil, .Out_Of_Memory
}
alignment_offset := calc_alignment_offset(block, uintptr(alignment))
size, size_ok := safe_add(min_size, alignment_offset)
if !size_ok {
err = .Out_Of_Memory
return
}
if to_be_used, ok := safe_add(block.used, size); !ok || to_be_used > block.reserved {
err = .Out_Of_Memory
return
}
assert(block.committed <= block.reserved)
do_commit_if_necessary(block, size) or_return
data = block.base[block.used+alignment_offset:][:min_size]
block.used += size
return
}
memory_block_dealloc :: proc(block_to_free: ^Memory_Block) {
if block := (^Platform_Memory_Block)(block_to_free); block != nil {
platform_memory_free(block)
}
}
@(private, require_results)
safe_add :: #force_inline proc "contextless" (x, y: uint) -> (uint, bool) {
z, did_overflow := intrinsics.overflow_add(x, y)
return z, !did_overflow
}
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