NAME<\/a>
SYNOPSIS<\/a>
DESCRIPTION<\/a>
RETURN VALUE<\/a>
ERRORS<\/a>
EXAMPLES<\/a>
APPLICATION USAGE<\/a>
RATIONALE<\/a>
FUTURE DIRECTIONS<\/a>
SEE ALSO<\/a>
COPYRIGHT<\/a> <\/p>\n
\n
PROLOG <\/a> <\/h2>\nThis manual page is part of the POSIX Programmer\u2019s Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.<\/p>\n
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<\/p>\n
NAME <\/a> <\/h2>\nilogb, ilogbf, ilogbl \u2014 return an unbiased exponent<\/p>\n
SYNOPSIS <\/a> <\/h2>\n#include <\/p>\nint ilogb(double x<\/i>);
int ilogbf(float x<\/i>);
int ilogbl(long double x<\/i>);<\/p>\nDESCRIPTION <\/a> <\/h2>\nThe functionality described on this reference page is aligned with the ISO\u00a0C standard. Any conflict between the requirements described here and the ISO\u00a0C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO\u00a0C standard.<\/p>\n
These functions shall return the exponent part of their argument x<\/i>. Formally, the return value is the integral part of $log sub{r}|x|$ as a signed integral value, for non-zero x<\/i>, where r<\/i> is the radix of the machine\u2019s floating-point arithmetic, which is the value of FLT_RADIX defined in <\/i>.<\/p>\nAn application wishing to check for error situations should set errno<\/i> to zero and call feclearexcept<\/i>(FE_ALL_EXCEPT) before calling these functions. On return, if errno<\/i> is non-zero or fetestexcept<\/i>(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.<\/p>\nRETURN VALUE <\/a> <\/h2>\nUpon successful completion, these functions shall return the exponent part of x<\/i> as a signed integer value. They are equivalent to calling the corresponding logb<\/i>() function and casting the returned value to type int<\/b>.<\/p>\n
If x<\/i> is 0, the value FP_ILOGB0 shall be returned. On XSI-conformant systems, a domain error shall occur;
otherwise, a domain error may occur.<\/p>\n
If x<\/i> is \u00b1Inf, the value {INT_MAX} shall be returned. On XSI-conformant systems, a domain error shall occur;
otherwise, a domain error may occur.<\/p>\n
If x<\/i> is a NaN, the value FP_ILOGBNAN shall be returned. On XSI-conformant systems, a domain error shall occur;
otherwise, a domain error may occur.<\/p>\n
If the correct value is greater than {INT_MAX}, a domain error shall occur and an unspecified value shall be returned. On XSI-conformant systems, a domain error shall occur and {INT_MAX} shall be returned.<\/p>\n
If the correct value is less than {INT_MIN}, a domain error shall occur and an unspecified value shall be returned. On XSI-conformant systems, a domain error shall occur and {INT_MIN} shall be returned.<\/p>\n
ERRORS <\/a> <\/h2>\nThese functions shall fail if:
Domain\u00a0Error<\/p>\n
The correct value is not representable as an integer.<\/p>\n
The x<\/i> argument is zero, NaN, or \u00b1Inf.<\/p>\n
If the integer expression (math_errhandling<\/i> & MATH_ERRNO) is non-zero, then errno<\/i> shall be set to [EDOM]<\/b>. If the integer expression (math_errhandling<\/i> & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.<\/p>\n
These functions may fail if:
Domain\u00a0Error<\/p>\n
The x<\/i> argument is zero, NaN, or \u00b1Inf.<\/p>\n
If the integer expression (math_errhandling<\/i> & MATH_ERRNO) is non-zero, then errno<\/i> shall be set to [EDOM]<\/b>. If the integer expression (math_errhandling<\/i> & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.<\/p>\n
The following sections are informative.<\/i><\/p>\nEXAMPLES <\/a> <\/h2>\nNone.<\/p>\n
APPLICATION USAGE <\/a> <\/h2>\nOn error, the expressions (math_errhandling<\/i> & MATH_ERRNO) and (math_errhandling<\/i> & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.<\/p>\nRATIONALE <\/a> <\/h2>\nThe errors come from taking the expected floating-point value and converting it to int<\/b>, which is an invalid operation in IEEE\u00a0Std\u00a0754-1985 (since overflow, infinity, and NaN are not representable in a type int<\/b>), so should be a domain error.<\/p>\n
There are no known implementations that overflow. For overflow to happen, {INT_MAX} must be less than LDBL_MAX_EXP*log2<\/i>(FLT_RADIX) or {INT_MIN} must be greater than LDBL_MIN_EXP*log2<\/i>(FLT_RADIX) if subnormals are not supported, or {INT_MIN} must be greater than (LDBL_MIN_EXP-LDBL_MANT_DIG)*log2<\/i>(FLT_RADIX) if subnormals are supported.<\/p>\nFUTURE DIRECTIONS <\/a> <\/h2>\nNone.<\/p>\n
SEE ALSO <\/a> <\/h2>\nfeclearexcept<\/i>(), fetestexcept<\/i>(), logb<\/i>(), scalbln<\/i>()<\/p>\n
<\/p>\nilogb, ilogbf, ilogbl \u2014 return an unbiased exponent<\/p>\n
SYNOPSIS <\/a> <\/h2>\n#include <\/p>\nint ilogb(double x<\/i>);
int ilogbf(float x<\/i>);
int ilogbl(long double x<\/i>);<\/p>\nDESCRIPTION <\/a> <\/h2>\nThe functionality described on this reference page is aligned with the ISO\u00a0C standard. Any conflict between the requirements described here and the ISO\u00a0C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO\u00a0C standard.<\/p>\n
These functions shall return the exponent part of their argument x<\/i>. Formally, the return value is the integral part of $log sub{r}|x|$ as a signed integral value, for non-zero x<\/i>, where r<\/i> is the radix of the machine\u2019s floating-point arithmetic, which is the value of FLT_RADIX defined in <\/i>.<\/p>\nAn application wishing to check for error situations should set errno<\/i> to zero and call feclearexcept<\/i>(FE_ALL_EXCEPT) before calling these functions. On return, if errno<\/i> is non-zero or fetestexcept<\/i>(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.<\/p>\nRETURN VALUE <\/a> <\/h2>\nUpon successful completion, these functions shall return the exponent part of x<\/i> as a signed integer value. They are equivalent to calling the corresponding logb<\/i>() function and casting the returned value to type int<\/b>.<\/p>\n
If x<\/i> is 0, the value FP_ILOGB0 shall be returned. On XSI-conformant systems, a domain error shall occur;
otherwise, a domain error may occur.<\/p>\n
If x<\/i> is \u00b1Inf, the value {INT_MAX} shall be returned. On XSI-conformant systems, a domain error shall occur;
otherwise, a domain error may occur.<\/p>\n
If x<\/i> is a NaN, the value FP_ILOGBNAN shall be returned. On XSI-conformant systems, a domain error shall occur;
otherwise, a domain error may occur.<\/p>\n
If the correct value is greater than {INT_MAX}, a domain error shall occur and an unspecified value shall be returned. On XSI-conformant systems, a domain error shall occur and {INT_MAX} shall be returned.<\/p>\n
If the correct value is less than {INT_MIN}, a domain error shall occur and an unspecified value shall be returned. On XSI-conformant systems, a domain error shall occur and {INT_MIN} shall be returned.<\/p>\n
ERRORS <\/a> <\/h2>\nThese functions shall fail if:
Domain\u00a0Error<\/p>\n
The correct value is not representable as an integer.<\/p>\n
The x<\/i> argument is zero, NaN, or \u00b1Inf.<\/p>\n
If the integer expression (math_errhandling<\/i> & MATH_ERRNO) is non-zero, then errno<\/i> shall be set to [EDOM]<\/b>. If the integer expression (math_errhandling<\/i> & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.<\/p>\n
These functions may fail if:
Domain\u00a0Error<\/p>\n
The x<\/i> argument is zero, NaN, or \u00b1Inf.<\/p>\n
If the integer expression (math_errhandling<\/i> & MATH_ERRNO) is non-zero, then errno<\/i> shall be set to [EDOM]<\/b>. If the integer expression (math_errhandling<\/i> & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.<\/p>\n
The following sections are informative.<\/i><\/p>\nEXAMPLES <\/a> <\/h2>\nNone.<\/p>\n
APPLICATION USAGE <\/a> <\/h2>\nOn error, the expressions (math_errhandling<\/i> & MATH_ERRNO) and (math_errhandling<\/i> & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.<\/p>\nRATIONALE <\/a> <\/h2>\nThe errors come from taking the expected floating-point value and converting it to int<\/b>, which is an invalid operation in IEEE\u00a0Std\u00a0754-1985 (since overflow, infinity, and NaN are not representable in a type int<\/b>), so should be a domain error.<\/p>\n
There are no known implementations that overflow. For overflow to happen, {INT_MAX} must be less than LDBL_MAX_EXP*log2<\/i>(FLT_RADIX) or {INT_MIN} must be greater than LDBL_MIN_EXP*log2<\/i>(FLT_RADIX) if subnormals are not supported, or {INT_MIN} must be greater than (LDBL_MIN_EXP-LDBL_MANT_DIG)*log2<\/i>(FLT_RADIX) if subnormals are supported.<\/p>\nFUTURE DIRECTIONS <\/a> <\/h2>\nNone.<\/p>\n
SEE ALSO <\/a> <\/h2>\nfeclearexcept<\/i>(), fetestexcept<\/i>(), logb<\/i>(), scalbln<\/i>()<\/p>\n
int ilogb(double x<\/i>); The functionality described on this reference page is aligned with the ISO\u00a0C standard. Any conflict between the requirements described here and the ISO\u00a0C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO\u00a0C standard.<\/p>\n These functions shall return the exponent part of their argument x<\/i>. Formally, the return value is the integral part of $log sub{r}|x|$ as a signed integral value, for non-zero x<\/i>, where r<\/i> is the radix of the machine\u2019s floating-point arithmetic, which is the value of FLT_RADIX defined in An application wishing to check for error situations should set errno<\/i> to zero and call feclearexcept<\/i>(FE_ALL_EXCEPT) before calling these functions. On return, if errno<\/i> is non-zero or fetestexcept<\/i>(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.<\/p>\n Upon successful completion, these functions shall return the exponent part of x<\/i> as a signed integer value. They are equivalent to calling the corresponding logb<\/i>() function and casting the returned value to type int<\/b>.<\/p>\n If x<\/i> is 0, the value FP_ILOGB0 shall be returned. On XSI-conformant systems, a domain error shall occur; If x<\/i> is \u00b1Inf, the value {INT_MAX} shall be returned. On XSI-conformant systems, a domain error shall occur; If x<\/i> is a NaN, the value FP_ILOGBNAN shall be returned. On XSI-conformant systems, a domain error shall occur; If the correct value is greater than {INT_MAX}, a domain error shall occur and an unspecified value shall be returned. On XSI-conformant systems, a domain error shall occur and {INT_MAX} shall be returned.<\/p>\n If the correct value is less than {INT_MIN}, a domain error shall occur and an unspecified value shall be returned. On XSI-conformant systems, a domain error shall occur and {INT_MIN} shall be returned.<\/p>\n These functions shall fail if: The correct value is not representable as an integer.<\/p>\n The x<\/i> argument is zero, NaN, or \u00b1Inf.<\/p>\n If the integer expression (math_errhandling<\/i> & MATH_ERRNO) is non-zero, then errno<\/i> shall be set to [EDOM]<\/b>. If the integer expression (math_errhandling<\/i> & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.<\/p>\n These functions may fail if: The x<\/i> argument is zero, NaN, or \u00b1Inf.<\/p>\n If the integer expression (math_errhandling<\/i> & MATH_ERRNO) is non-zero, then errno<\/i> shall be set to [EDOM]<\/b>. If the integer expression (math_errhandling<\/i> & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.<\/p>\n The following sections are informative.<\/i><\/p>\n None.<\/p>\n On error, the expressions (math_errhandling<\/i> & MATH_ERRNO) and (math_errhandling<\/i> & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.<\/p>\n The errors come from taking the expected floating-point value and converting it to int<\/b>, which is an invalid operation in IEEE\u00a0Std\u00a0754-1985 (since overflow, infinity, and NaN are not representable in a type int<\/b>), so should be a domain error.<\/p>\n There are no known implementations that overflow. For overflow to happen, {INT_MAX} must be less than LDBL_MAX_EXP*log2<\/i>(FLT_RADIX) or {INT_MIN} must be greater than LDBL_MIN_EXP*log2<\/i>(FLT_RADIX) if subnormals are not supported, or {INT_MIN} must be greater than (LDBL_MIN_EXP-LDBL_MANT_DIG)*log2<\/i>(FLT_RADIX) if subnormals are supported.<\/p>\n None.<\/p>\n feclearexcept<\/i>(), fetestexcept<\/i>(), logb<\/i>(), scalbln<\/i>()<\/p>\n
int ilogbf(float x<\/i>);
int ilogbl(long double x<\/i>);<\/p>\nDESCRIPTION <\/a> <\/h2>\n
RETURN VALUE <\/a> <\/h2>\n
otherwise, a domain error may occur.<\/p>\n
otherwise, a domain error may occur.<\/p>\n
otherwise, a domain error may occur.<\/p>\nERRORS <\/a> <\/h2>\n
Domain\u00a0Error<\/p>\n
Domain\u00a0Error<\/p>\nEXAMPLES <\/a> <\/h2>\n
APPLICATION USAGE <\/a> <\/h2>\n
RATIONALE <\/a> <\/h2>\n
FUTURE DIRECTIONS <\/a> <\/h2>\n
SEE ALSO <\/a> <\/h2>\n