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tevador
2018-12-31 19:27:31 +01:00
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## RandomX virtual machine
RandomX is intended to be run efficiently on a general-purpose CPU. The virtual machine (VM) which runs RandomX code attempts to simulate a generic CPU using the following set of components:
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#### Stack
To simulate function calls, the VM uses a stack structure. The program interacts with the stack using the CALL and RET instructions. The stack has unlimited size and each stack element is 64 bits wide.
*Although there is no explicit limit of the stack size, the maximum theoretical size of the stack is 16 MiB for a program that contains only unconditional CALL instructions (the probability of randomly generating such program is about 5×10<sup>-912</sup>). In reality, the stack size will rarely exceed 1 MiB.*
*Although there is no explicit limit of the stack size, the maximum theoretical size of the stack is 16 MiB. Most programs will use around 4 KiB of stack.*
#### Register file
The VM has 8 integer registers `r0`-`r7` and 8 floating point registers `f0`-`f7`. All registers are 64 bits wide.
The VM has 8 integer registers `r0`-`r7` and 8 floating point registers `f0`-`f7`. The integer registers are 64 bits wide. The floating point registers are 128 bits wide and each stores two packed double precision numbers.
*The number of registers is low enough so that they can be stored in actual hardware registers on most CPUs.*
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The arithmetic logic unit (ALU) performs integer operations. The ALU can perform binary integer operations from 7 groups (addition, subtraction, multiplication, division, bitwise operations, shift, rotation) with operand sizes of 64 or 32 bits.
#### FPU
The floating-point unit performs IEEE-754 compliant math using 64-bit double precision floating point numbers. Five basic operations are available: addition, subtraction, multiplication, division and square root.
The floating-point unit performs IEEE-754 compliant math using 64-bit double precision floating point numbers. Five basic operations are available: addition, subtraction, multiplication, division and square root. All operations work with two packed double precision numbers.
#### Binary encoding
The VM stores and loads all data in little-endian byte order. Signed numbers are represented using two's complement.
The VM stores and loads all data in little-endian byte order. Signed integer numbers are represented using two's complement.