RandomX is a proof-of-work (PoW) algorithm that is optimized for general-purpose CPUs. RandomX uses random code execution (hence the name) together with several memory-hard techniques to achieve the following goals:
RandomX behaves like a keyed hashing function: it accepts a key `K` and arbitrary input `H` and produces a 256-bit result `R`. Under the hood, RandomX utilizes a virtual machine that executes programs in a special instruction set that consists of a mix of integer math, floating point math and branches. These programs can be translated into the CPU's native machine code on the fly. Example of a RandomX program translated into x86-64 assembly is [program.asm](doc/program.asm). A portable interpreter mode is also provided.
RandomX is written in C++11 and builds a static library with a C API provided by header file [randomx.h](src/randomx.h). Minimal API usage example is provided in [api-example1.c](src/tests/api-example1.c). The reference code includes a `benchmark` executable for testing.
* The key `K` is selected to be the hash of a block in the blockchain - this block is called the 'key block'. For optimal mining and verification performance, the key should change every 2048 blocks (~2.8 days) and there should be a delay of 64 blocks (~2 hours) between the key block and the change of the key `K`. This can be achieved by changing the key when `blockHeight % 2048 == 64` and selecting key block such that `keyBlockHeight % 2048 == 0`.
If you wish to use RandomX as a PoW algorithm for your cryptocurrency, we strongly recommend not using the [default parameters](src/configuration.h) and change at least the following:
* Size of the Dataset (`RANDOMX_DATASET_BASE_SIZE` and `RANDOMX_DATASET_EXTRA_SIZE`).
* Scratchpad size (`RANDOMX_SCRATCHPAD_L3`, `RANDOMX_SCRATCHPAD_L2` and `RANDOMX_SCRATCHPAD_L1`).
* Instruction frequencies (parameters starting with `RANDOMX_FREQ_`).
RandomX was designed to be efficient on CPUs. Designing an algorithm compatible with both CPUs and GPUs brings many limitations and ultimately decreases ASIC resistance.
GPUs are expected to be at a disadvantage when running RandomX, but the exact performance has not been determined yet due to lack of a working GPU implementation.
A rough estimate for AMD Vega 56 GPU gave an upper limit of 1200 H/s, comparable to a quad core CPU (details in issue [#24](https://github.com/tevador/RandomX/issues/24)).
Efficient mining requires more than 2 GiB of memory, which is difficult to hide in an infected computer and disqualifies many low-end machines such as IoT devices. Web mining is nearly impossible due to the large memory requirement and low performance in interpreted mode.
RandomX uses only operations that are guaranteed to give correctly rounded results by the [IEEE 754](https://en.wikipedia.org/wiki/IEEE_754) standard: addition, subtraction, multiplication, division and square root. Special care is taken to avoid corner cases such as NaN values or denormals.
The author of RandomX declares no competing financial interest in RandomX adoption, other than being a holder or Monero. The development of RandomX was funded from the author's own pocket with only the help listed above.
