Developer Reference

  • 2021.1
  • 12/04/2020
  • Public Content

Conditional Numerical Reproducibility Control

The CNR mode of
Intel® oneAPI Math Kernel Library
ensures bitwise reproducible results from run to run of
Intel® oneAPI Math Kernel Library
functions on a fixed number of threads for a specific Intel instruction set architecture (ISA) under the following conditions:
  • Calls to
    Intel® oneAPI Math Kernel Library
    occur in a single executable
  • The number of computational threads used by the library does not change in the run
Intel® oneAPI Math Kernel Library
offers both functions and environment variables to support conditional numerical reproducibility. See the
Intel® oneAPI Math Kernel Library
Developer Guide
for more information on bitwise reproducible results of computations and for details about the environment variables.
The support functions enable you to configure the CNR mode and also provide information on the current and optimal CNR branch on your system. Usage Examples for CNR Support Functions illustrate usage of these functions.
Call the functions that define the behavior of CNR before any of the math library functions that they control.
Intel® oneAPI Math Kernel Library
provides named constants for use as input and output parameters of the functions instead of integer values. SeeNamed Constants for CNR Control for a list of the named constants.
Although you can configure the CNR mode using either the support functions or the environment variables, the functions offer more flexible configuration and control than the environment variables. Settings specified by the functions take precedence over the settings specified by the environment variables.
Intel® oneAPI Math Kernel Library
in the CNR mode only in case a need for bitwise reproducible results is critical. Otherwise, run
Intel® oneAPI Math Kernel Library
as usual to avoid performance degradation.
While you can supply unaligned input and output data to
Intel® oneAPI Math Kernel Library
functions running in the CNR mode, use of aligned data is recommended. Refer toReproducibility Conditions for more details.
Optimization Notice
Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.
Notice revision #20110804
This notice covers the following instruction sets: SSE2, SSE4.2, AVX2, AVX-512.

Product and Performance Information


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