fimf-accuracy-bits, Qimf-accuracy-bits

Defines the relative error for math library function results, including division and square root.

Syntax

Linux:

-fimf-accuracy-bits=bits[:funclist]

Windows:

/Qimf-accuracy-bits:bits[:funclist]

Arguments

bits

Is a positive, floating-point number indicating the number of correct bits the compiler should use.

The format for the number is [digits] [.digits] [ { e | E }[sign]digits].

funclist

Is an optional list of one or more math library functions to which the attribute should be applied. 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-accuracy-bits=23:sin,sinf (or /Qimf-accuracy-bits:23:sin,sinf) to specify the relative error 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-accuracy-bits=10.0:/f or /Qimf-accuracy-bits:10.0:/f.

Default

-fimf-precision=medium or /Qimf-precision: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 defines the relative error, measured by the number of correct bits, for math library function results.

The following formula is used to convert bits into ulps: ulps = 2p-1-bits, where p is the number of the target format mantissa bits (24, 53, and 64 for single, double, and long double, respectively).

This option can affect run-time performance and the accuracy of results.

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 the following:

  • -fimf-accuracy-bits=23:sinf,cosf,logf or /Qimf-accuracy-bits:23:sinf,cosf,logf

  • -fimf-accuracy-bits=52:sqrt,/,trunc or /Qimf-accuracy-bits:52:sqrt,/,trunc

  • -fimf-accuracy-bits=10:powf or /Qimf-accuracy-bits:10:powf

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:

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

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

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

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:

  • -fp-model (Linux) 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.

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

IDE Equivalent

None

Alternate Options

None

Para obtener información más completa sobre las optimizaciones del compilador, consulte nuestro Aviso de optimización.