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Pointer formats are known as near, far, or huge. Near pointers are 16-bit offsets within the reference segment, i.e. DS for data and CS for code. They are the fastest pointers, but are limited to point to 64 KB of memory (to the associated segment of the data type). Near pointers can be held in registers (typically SI and DI).
Here is a simple example of index register use in assembly language pseudo-code that sums a 100 entry array of 4-byte words: Clear_accumulator Load_index 400,index2 //load 4*array size into index register 2 (index2) loop_start : Add_word_to_accumulator array_start,index2 //Add to AC the word at the address (array_start + index2) Branch_and_decrement_if_index_not_zero loop_start,4,index2 //loop ...
A pointer a pointing to the memory address associated with a variable b, i.e., a contains the memory address 1008 of the variable b.In this diagram, the computing architecture uses the same address space and data primitive for both pointers and non-pointers; this need not be the case.
Each can be accessed as two separate bytes (thus BX's high byte can be accessed as BH and low byte as BL). Two pointer registers have special roles: SP (stack pointer) points to the "top" of the stack, and BP (base pointer) is often used to point at some other place in the stack, typically above the local variables (see frame pointer).
SS:SP (SS is Stack Segment, SP is Stack Pointer) points to the address of the top of the stack, i.e. the most recently pushed byte. SS:BP (SS is Stack Segment, BP is Stack Frame Pointer) points to the address of the top of the stack frame, i.e. the base of the data area in the call stack for the currently active subprogram.
The mechanism was overhauled in 2013; questions edited after being put "on hold" now appear in a review queue. [31] Jeff Atwood stated in 2010 that duplicate questions are not seen as a problem but rather they constitute an advantage if such additional questions drive extra traffic to the site by multiplying relevant keyword hits in search engines.
Front panel of an IBM 701 computer introduced in 1952. Lights in the middle display the contents of various registers. The instruction counter is at the lower left.. The program counter (PC), [1] commonly called the instruction pointer (IP) in Intel x86 and Itanium microprocessors, and sometimes called the instruction address register (IAR), [2] [1] the instruction counter, [3] or just part of ...
The OpenVMS Calling Standard on x86-64 is based on the System V ABI with some extensions needed for backwards compatibility. [27] The first six integer or pointer arguments are passed in registers RDI, RSI, RDX, RCX, R8, R9 (R10 is used as a static chain pointer in case of nested functions [ 28 ] : 21 ), while XMM0, XMM1, XMM2, XMM3, XMM4, XMM5 ...