A zero register is a processor register that always returns the value zero and has no effect when it is written to. It is found in instruction set architectures including the CDC 6600, System/360 and ARM64, among others.
Zero appears as a constant in many instructions, notably "branch if zero", and optimizing these instructions can have a positive benefit on performance. Some architectures accomplish this with dedicated opcodes, specialized variations of their basic instructions. Implementing these requires additional logic in the instruction decoder. The zero register can accomplish the same effect without requiring new opcodes, although at the cost of dedicating a register to this feature, which may have negative impact for architectures with limited number of registers.
The x86 architecture has no zero register, ARM added a zero register for ARM64. The RISC-V architecture includes one with the register name "x0" and the ABI name "zero"; the reason for this inclusion is stated as "Dedicating a register to zero is surprisingly a large factor in simplifying the RISC-V ISA."[1]
^Patterson, David. The RISC-V Reader: An Open Architecture Atlas (Beta Ed., 0.0.1 ed.). p. 18.
A zeroregister is a processor register that always returns the value zero and has no effect when it is written to. It is found in instruction set architectures...
Branch_and_decrement_if_index_not_zero loop_start,4,index2 //loop decrementing by 4 until index register is zero For loop The term X-registers was also used for accumulators...
often stored in a dedicated register, typically called status register or flag register, along with other flags. The zero flag is typically abbreviated...
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number of registers is a power of two, e.g. 8, 16, 32. In some cases a hardwired-to-zero pseudo-register is included, as "part" of register files of architectures...
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...
MIPS), the first or last register in the integer register file is a pseudo-register in that it is hardwired to always return zero when read (mostly to simplify...
Zero page addressing now has mostly historical significance, since the developments in integrated circuit technology have made adding more registers to...
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2017. AVX uses sixteen YMM registers to perform a single instruction on multiple pieces of data (see SIMD). Each YMM register can hold and do simultaneous...
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will act like an "X" report, except that counters will be reset to zero. Registers will typically feature a numerical pad, QWERTY or custom keyboard,...
of ebx with zeroes. On x64, most instructions that write to the entirety of lower 32 bits of any of the general-purpose registers will zero the upper half...
many countries, kilometre zero (also written km 0) or similar terms in other languages (also known as zero mile marker, zero milepost, control stations...
31 general-purpose registers as: x31 (SP): Stack pointer or a zeroregister, depending on context. x30 (LR): Procedure link register, used to return from...
domain was registered on 11 January 2009 under the name Krassimir Ivandjiiski of ABC Media Ltd, the father of Daniel Ivandjiiski, who founded Zero Hedge....
in a memory register), but the stored value is not large enough to result in a non-zero most significant digit. The count leading zeros operation efficiently...
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8/16-bit Zero register '0' to speed up operations using a zero constant. This register always reads zero and writes to it are ignored. Mode register 'MD', a...
status register, flag register, or condition code register (CCR) is a collection of status flag bits for a processor. Examples of such registers include...
operand. The debug registers are privileged resources; the MOV instructions that access them can only be executed at privilege level zero. An attempt to read...
at zero but the minimum descriptor index that can be loaded into a segment register is 1; the value 0 is reserved to represent a segment register that...
connects the output of the last shift register to the first shift register input and circulates a single one (or zero) bit around the ring. A twisted ring...
short-cut to setting the value of a register to zero. Performing XOR on a value against itself always yields zero, and on many architectures this operation...
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