Size: a a a
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A
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Адресная арифметика появилась как логичное продолжение идеи указателей, унаследованной от ассемблерных языков: в последних имеется возможность указать некое смещение от текущего положения.
int* p; // Допустим, p указывает на адрес 200
p++; // После инкрементации она указывает на 200 + sizeof(int) = 204
p--; // Сейчас она вновь указывает на 200.
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a: dd str
str: db '123', 0
str2: db '123', 0
add dword[a], 4 ; a указывает на str2
sub dword[a], 4 ; a указывает снова на str
E
sizeof(int)?d
--------b-15E820-----------------------------
INT 15 - newer BIOSes - GET SYSTEM MEMORY MAP
AX = E820h
EAX = 0000E820h
EDX = 534D4150h ('SMAP')
EBX = continuation value or 00000000h to start at beginning of map
ECX = size of buffer for result, in bytes (should be >= 20 bytes)
ES:DI -> buffer for result (see #00581)
Return: CF clear if successful
EAX = 534D4150h ('SMAP')
ES:DI buffer filled
EBX = next offset from which to copy or 00000000h if all done
ECX = actual length returned in bytes
CF set on error
AH = error code (86h) (see #00496 at INT 15/AH=80h)
Notes: originally introduced with the Phoenix BIOS v4.0, this function is
now supported by most newer BIOSes, since various versions of Windows
call it to find out about the system memory
a maximum of 20 bytes will be transferred at one time, even if ECX is
higher; some BIOSes (e.g. Award Modular BIOS v4.50PG) ignore the
value of ECX on entry, and always copy 20 bytes
some BIOSes expect the high word of EAX to be clear on entry, i.e.
EAX=0000E820h
if this function is not supported, an application should fall back
to AX=E802h, AX=E801h, and then AH=88h
the BIOS is permitted to return a nonzero continuation value in EBX
and indicate that the end of the list has already been reached by
returning with CF set on the next iteration
this function will return base memory and ISA/PCI memory contiguous
with base memory as normal memory ranges; it will indicate
chipset-defined address holes which are not in use and motherboard
memory-mapped devices, and all occurrences of the system BIOS as
reserved; standard PC address ranges will not be reported
SeeAlso: AH=C7h,AX=E801h"Phoenix",AX=E881h,MEM xxxxh:xxx0h"ACPI"
Format of Phoenix BIOS system memory map address range descriptor:
Offset Size Description (Table 00580)
00h QWORD base address
08h QWORD length in bytes
10h DWORD type of address range (see #00581)
(Table 00581)
Values for System Memory Map address type:
01h memory, available to OS
02h reserved, not available (e.g. system ROM, memory-mapped device)
03h ACPI Reclaim Memory (usable by OS after reading ACPI tables)
04h ACPI NVS Memory (OS is required to save this memory between NVS
sessions)
other not defined yet -- treat as Reserved
SeeAlso: #00580d
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