# fimf-precision, Qimf-precision

Lets you specify a level of accuracy (precision) that the compiler should use when determining which math library functions to use.

## Syntax

Linux: | -fimf-precision[=value[:funclist]]

macOS: | -fimf-precision[=value[:funclist]]

Windows: | /Qimf-precision[:value[:funclist]]

Optional argument funclist is not supported for ifx.

## Arguments

value | Is one of the following values denoting the desired accuracy:
high | This is equivalent to max-error = 1.0.
medium | This is equivalent to max-error = 4; this is the default setting if the option is specified and value is omitted.
low | This is equivalent to accuracy-bits = 11 for single-precision functions; accuracy-bits = 26 for double-precision functions.
Linux and macOS In the above explanations, max-error means option -fimf-max-error; accuracy-bits means option -fimf-accuracy-bits. Windows In the above explanations, max-error means option /Qimf-max-error (Windows*); accuracy-bits means option /Qimf-accuracy-bits.
funclist | Is an optional list of one or more math library functions to which the attribute should be applied. At this time, funclist is not supported for ifx. Do not specify the standard Fortran name of the math function; you must specify the actual math library name. If you specify more than one function, they must be separated with commas. Precision-specific variants like sin and sinf are considered different functions, so you would need to use -fimf-precision=high:sin,sinf (or /Qimf-precision:high:sin,sinf) to specify high precision for both the single-precision and double-precision sine functions. You also can specify the symbol /f to denote single-precision divides, symbol / to denote double-precision divides, symbol /l to denote extended-precision divides, and symbol /q to denote quad-precision divides. For example you can specify -fimf-precision=low:/ or /Qimf-precision:low:/ and -fimf-precision=low:/f or /Qimf-precision:low:/f.

## Default

medium | The compiler uses medium precision when calling math library functions. Note that other options can affect precision; see below for details.

## Description

This option lets you specify a level of accuracy (precision) that the compiler should use when determining which math library functions to use.

This option can be used to improve run-time performance if reduced accuracy is sufficient for the application, or it can be used to increase the accuracy of math library functions selected by the compiler.

In general, using a lower precision can improve run-time performance and using a higher precision may reduce run-time performance.

If you need to define the accuracy for a math function of a certain precision, specify the function name of the precision that you need. For example, if you want double precision, you can specify :sin; if you want single precision, you can specify :sinf, as in -fimf-precision=low:sin or /Qimf-precision:low:sin, or -fimf-precision=high:sqrtf or /Qimf-precision:high:sqrtf.

If you do not specify any function names, then the setting applies to all functions (and to all precisions). However, as soon as you specify an individual function name, the setting applies only to the function of corresponding precision. So, for example, sinf applies only to the single-precision sine function, sin applies only to the double-precision sine function, sinl applies only to the extended-precision sine function, etc.

There are three options you can use to express the maximum relative error. They are as follows:

Linux and macOS

- -fimf-precision

- -fimf-max-error

- -fimf-accuracy-bits

Windows

- /Qimf-precision

- /Qimf-max-error

- /Qimf-accuracy-bits

If more than one of these options are specified, the default value for the maximum relative error is determined by the last one specified on the command line.

If none of the above options are specified, the default values for the maximum relative error are determined by the setting of the following options:

- [Q]fast-transcendentals (ifort only)

- [Q]prec-div (ifort only)

- [Q]prec-sqrt (ifort only)

- -fp-model (Linux and macOS) or /fp (Windows)

### Note

Many routines in libraries LIBM (Math Library) and SVML (Short Vector Math Library) are more highly optimized for Intel® microprocessors than for non-Intel microprocessors.

### Note

The standard Fortran names for the various math intrinsic functions do not match the math library names of the math intrinsic functions. You must find the actual math library name that is generated for the relevant Fortran math intrinsic.

One way to do this is to generate assembly code by using one of the following options:

Linux and macOS

-S

Windows

/Fa or /S

The assembly code will show the actual math library name.

For example, if you create a program that contains a call to SIN(x) where x is declared as REAL(KIND=4) and then use option S to produce assembly code for the program, the assembly code will show a call to sinf.

To specify a level of accuracy for the single-precision sine function, you should specify:

Linux and macOS

-fimf-precision=sinf

Windows

/Qimf-precision:sinf

### Note

This option only applies to host compilation. When offloading is enabled, it does not impact device-specific compilation. Offloading can only be enabled when using ifx.

Product and Performance Information
Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex. Notice revision #20201201

## IDE Equivalent

None

## Alternate Options

None

Parent topic: Floating-Point Options

## See Also

fimf-absolute-error, Qimf-absolute-error compiler option
fimf-accuracy-bits, Qimf-accuracy-bits compiler option
fimf-arch-consistency, Qimf-arch-consistency compiler option
fimf-domain-exclusion, Qimf-domain-exclusion compiler option
fimf-max-error, Qimf-max-error compiler option
fast-transcendentals, Qfast-transcendentals compiler option
prec-div, Qprec-div compiler option
prec-sqrt, Qprec-sqrt compiler option
fp-model, fp compiler option
fimf-use-svml_Qimf-use-svml compiler option