RandomX has 45 customizable parameters (see table below). We recommend each project using RandomX to select a unique configuration to prevent network attacks from hashpower rental services.
These parameters can be modified in source file [configuration.h](../src/configuration.h).
|parameter|description|default value|
|---------|-----|-------|
|`RANDOMX_ARGON_MEMORY`|The number of 1 KiB Argon2 blocks in the Cache| `262144`|
|`RANDOMX_ARGON_ITERATIONS`|The number of Argon2d iterations for Cache initialization|`3`|
|`RANDOMX_ARGON_LANES`|The number of parallel lanes for Cache initialization|`1`|
Not all of the parameters can be changed safely and most parameters have some contraints on what values can be selected (checked at compile-time).
**Disclaimer: The compile-time checks only prevent obviously broken configurations. Passing the checks does not imply that the configuration is safe and will not cause crashes or other issues. We recommend that each non-standard configuration is thoroughly tested before being deployed.**
The default value was tuned so that a high-performance superscalar CPU running at 2-4 GHz will execute SuperscalarHash in similar time it takes to load data from RAM (40-80 ns). Using a lower value will make Dataset generation (and light mode) more memory bound, while increasing this value will make Dataset generation (and light mode) more compute bound.
### RANDOMX_DATASET_BASE_SIZE
Dataset base size in bytes.
#### Permitted values
Integer powers of 2 in the range 64 - 4294967296 (inclusive).
#### Note
This constant affects the memory requirements in fast mode. Some values are unsafe depending on other parameters. See [Unsafe configurations](#unsafe-configurations).
### RANDOMX_DATASET_EXTRA_SIZE
Dataset extra size in bytes.
#### Permitted values
Non-negative integer divisible by 64.
#### Note
This constant affects the memory requirements in fast mode. Some values are unsafe depending on other parameters. See [Unsafe configurations](#unsafe-configurations).
Smaller values will make RandomX more DRAM-latency bound, while higher values will make RandomX more compute-bound. Some values are unsafe. See [Unsafe configurations](#unsafe-configurations).
### RANDOMX_PROGRAM_ITERATIONS
The number of iterations per program.
#### Permitted values
Any positive integer.
#### Notes
Time per hash increases linearly with this constant. Smaller values will increase the overhead of program compilation, while larger values may allow more time for optimizations. Some values are unsafe. See [Unsafe configurations](#unsafe-configurations).
### RANDOMX_PROGRAM_COUNT
The number of programs per hash.
#### Permitted values
Any positive integer.
#### Notes
Time per hash increases linearly with this constant. Some values are unsafe. See [Unsafe configurations](#unsafe-configurations).
### RANDOMX_JUMP_BITS
Jump condition mask size in bits.
#### Permitted values
Positive integers. The sum of `RANDOMX_JUMP_BITS` and `RANDOMX_JUMP_OFFSET` must not exceed 16.
#### Notes
This determines the jump probability of the CBRANCH instruction. The default value of 8 results in jump probability of <code>1/2<sup>8</sup> = 1/256</code>. Increasing this constant will decrease the rate of jumps (and vice versa).
### RANDOMX_JUMP_OFFSET
Jump condition mask offset in bits.
#### Permitted values
Non-negative integers. The sum of `RANDOMX_JUMP_BITS` and `RANDOMX_JUMP_OFFSET` must not exceed 16.
#### Notes
Since the low-order bits of RandomX registers are slightly biased, this offset moves the condition mask to higher bits, which are less biased. Using values smaller than the default may result in a slightly lower jump probability than the theoretical value calculated from `RANDOMX_JUMP_BITS`.
### RANDOMX_SCRATCHPAD_L3
RandomX Scratchpad size in bytes.
#### Permitted values
Any integer power of 2. Must be larger than or equal to `RANDOMX_SCRATCHPAD_L2`.
#### Notes
The default value of 2 MiB was selected to match the typical cache/core ratio of desktop processors. Using a lower value will make RandomX more core-bound, while using larger values will make the algorithm more latency-bound. Some values are unsafe depending on other parameters. See [Unsafe configurations](#unsafe-configurations).
### RANDOMX_SCRATCHPAD_L2
Scratchpad L2 size in bytes.
#### Permitted values
Any integer power of 2. Must be larger than or equal to `RANDOMX_SCRATCHPAD_L1`.
#### Notes
The default value of 256 KiB was selected to match the typical per-core L2 cache size of desktop processors. Using a lower value will make RandomX more core-bound, while using larger values will make the algorithm more latency-bound.
### RANDOMX_SCRATCHPAD_L1
Scratchpad L1 size in bytes.
#### Permitted values
Any integer power of 2. The minimum is 64 bytes.
#### Notes
The default value of 16 KiB was selected to be about half of the per-core L1 cache size of desktop processors. Using a lower value will make RandomX more core-bound, while using larger values will make the algorithm more latency-bound.
### RANDOMX_FREQ_*
Instruction frequencies (per 256 instructions).
#### Permitted values
There is a total of 29 different instructions. The sum of frequencies must be equal to 256.
Making changes to the default values is not recommended. The only exceptions are the instruction pairs IROR_R/IROL_R, FADD_R/FSUB_R and FADD_M/FSUB_M, which are functionally equivalent. Example of a safe custom configuration:
There are some configurations that are considered 'unsafe' because they affect the security of the algorithm against attacks. If the conditions listed below are not satisfied, the configuration is unsafe and a compilation error is emitted when building the RandomX library.
These checks can be disabled by definining `RANDOMX_UNSAFE` when building RandomX, e.g. by using `-DRANDOMX_UNSAFE` command line switch in GCC or MSVC. It is not recommended to disable these checks except for testing purposes.
