Developer Guide and Reference

ID 767251
Date 10/31/2024
Public
Document Table of Contents

fp-model, fp

Controls the semantics of floating-point calculations.

Syntax

Linux:

-fp-model=keyword

Windows:

/fp:keyword

Arguments

keyword

Specifies the semantics to be used. Possible values are:

precise

Disables optimizations that are not value-safe on floating-point data.

fast[=1|2]

Enables more aggressive optimizations on floating-point data.

If you specify fast with no number, it is equivalent to fast=1.

consistent

Disables optimizations that are not value-safe on floating-point data and disables contraction (FMA) and selects math library functions that produce consistent results across different microarchitectural implementations of the same architecture.

strict

Enables precise, disables contractions, and enables the property that allows modification of the floating-point environment.

source

Rounds intermediate results to source-defined precision.

Default

-fp-model=fast
or /fp:fast

The compiler uses more aggressive optimizations on floating-point calculations.

Description

This option controls the semantics of floating-point calculations.

The floating-point (FP) environment is a collection of registers that control the behavior of FP machine instructions and indicate the current FP status. The floating-point environment may include rounding-mode controls, exception masks, flush-to-zero controls, exception status flags, and other floating-point related features.

Option

Description

-fp-model=precise or /fp:precise

Tells the compiler to strictly adhere to value-safe optimizations when implementing floating-point calculations. It disables optimizations that can change the result of floating-point calculations, which is required for strict ANSI conformance.

These semantics ensure the reproducibility of floating-point computations for serial code, including code vectorized or auto-parallelized by the compiler, but they may slow performance. They do not ensure value safety or run-to-run reproducibility of other parallel code.

Run-to-run reproducibility for floating-point reductions in OpenMP* code may be obtained for a fixed number of threads through the KMP_DETERMINISTIC_REDUCTION environment variable. For more information about this environment variable, see topic "Supported Environment Variables".

The compiler assumes the default floating-point environment; you are not allowed to modify it.

-fp-model=fast[=1|2] or /fp:fast[=1|2]

Tells the compiler to use more aggressive optimizations when implementing floating-point calculations. These optimizations increase speed, but they may affect the accuracy or reproducibility of floating-point computations.

Specifying fast is the same as specifying fast=1.

Setting fast=1 (the default) recognizes and supports NaN and infinite values. Setting fast=2 does not; no NaN or infinite values will be used or produced.

Setting fast or fast=1 sets option assume nan_compares; setting fast=2 sets option assume nonan_compares.

-fp-model=consistent or /fp:consistent

Disables optimizations that are not value-safe on floating-point data and disables contraction (FMA) and selects math library functions that produce consistent results across different microarchitectural implementations of the same architecture.

For more information, see the article titled: Consistency of Floating-Point Results using the Intel® Compiler.

-fp-model=strict or /fp:strict

Tells the compiler to strictly adhere to value-safe optimizations when implementing floating-point calculations and enables floating-point exception semantics. This is the strictest floating-point model.

The compiler does not assume the default floating-point environment; you are allowed to modify it.

-fp-model=source or /fp:source

This option causes intermediate results to be rounded to the precision defined in the source code. It also implies keyword precise.

It sets options -fprotect-parens and /Qprotect-parens.

The compiler assumes the default floating-point environment; you are not allowed to modify it.

The -fp-model and /fp options determine the setting for the maximum allowable relative error for math library function results (max-error) if none of the following options are specified:

  • -fimf-accuracy-bits (Linux*) or /Qimf-accuracy-bits (Windows*)

  • -fimf-max-error (Linux) or /Qimf-max-error (Windows)

  • -fimf-precision (Linux) or /Qimf-precision (Windows)

Option -fp-model=fast (and /fp:fast) sets option -fimf-precision=medium (/Qimf-precision:medium) and option -fp-model=precise (and /fp:precise); it implies -fimf-precision=high (and /Qimf-precision:high).

NOTE:

This option cannot be used to change the default (source) precision for the calculation of intermediate results.

NOTE:

In Microsoft* Visual Studio, when you create a Visual Studio* Fortran project, option /fp:fast is set by default. It sets the floating-point model to use more aggressive optimizations when implementing floating-point calculations, which increase speed, but may affect the accuracy or reproducibility of floating-point computations. /fp:fast is the general default for the IDE project property for Floating Point Model.

Product and Performance Information

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

Notice revision #20201201

IDE Equivalent

Visual Studio: Floating Point > Floating Point Model

Floating Point > Reliable Floating Point Exceptions Model

Alternate Options

None