Developer Reference for Intel® oneAPI Math Kernel Library - C

Developer Reference

  • 2021.1
  • 12/04/2020
  • Public Content
Contents

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.
Use
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

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.