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These instructions are also available in 32-bit mode, in which they operate on 32-bit registers (eax, ebx, etc.) and values instead of their 16-bit (ax, bx, etc.) counterparts. The updated instruction set is grouped according to architecture ( i186 , i286 , i386 , i486 , i586 / i686 ) and is referred to as (32-bit) x86 and (64-bit) x86-64 (also ...
The x86 processors support five modes of operation for x86 code, Real Mode, Protected Mode, Long Mode, Virtual 86 Mode, and System Management Mode, in which some instructions are available and others are not. A 16-bit subset of instructions is available on the 16-bit x86 processors, which are the 8086, 8088, 80186, 80188, and 80286.
The BT x86 assembly language instruction stands for Bit Test and was added to the x86 instruction set with the 80386 processor. BT copies a bit from a given register to the carry flag. [1] Example: copy the third least significant bit from EAX to the carry flag
For example, in the tiny model CS=DS=SS, that is the program's code, data, and stack are all contained within a single 64 KB segment. In the small memory model DS=SS, so both data and stack reside in the same segment; CS points to a different code segment of up to 64 KB.
While what these instructions do is similar to bit level gather-scatter SIMD instructions, PDEP and PEXT instructions (like the rest of the BMI instruction sets) operate on general-purpose registers. [12] The instructions are available in 32-bit and 64-bit versions. An example using arbitrary source and selector in 32-bit mode is:
The FLAGS register is the status register that contains the current state of an x86 CPU.The size and meanings of the flag bits are architecture dependent. It usually reflects the result of arithmetic operations as well as information about restrictions placed on the CPU operation at the current time.
The basic unit of digital storage is a bit, storing a single 0 or 1. Many common instruction set architectures can address more than 8 bits of data at a time. For example, 32-bit x86 processors have 32-bit general-purpose registers and can handle 32-bit (4-byte) data in single instructions. However, data in memory may be of various lengths.
The former loads a 80-bit BCD integer into the FPU, while the latter writes a FPU value as a 80-bit integer value into the memory. Inside of the FPU, the values are stored as normal x87 extended-precision floats. Unlike the integer-facing versions, the two instructions remain available in long mode. [1] The 80-bit format is divided into the ...