NAME

ilogb, ilogbf, ilogbl, logb, logbf, logbl —

extract exponent

LIBRARY

Math Library (libm, -lm)

SYNOPSIS

#include <math.h>

int
ilogb(double x);

int
ilogbf(float x);

int
ilogbl(long double x);

double
logb(double x);

float
logbf(float x);

long double
logbl(long double x);

DESCRIPTION

ilogb(), ilogbf() and ilogbl() return x's exponent in integer format. ilogb(±infinity) returns INT_MAX, ilogb(±NaN) returns FP_ILOGBNAN, and ilogb(0) returns FP_ILOGB0.

logb(x), logbf(x), and logbl(x) return x's exponent in floating-point format with the same precision as x. logb(±infinity) returns +infinity, and logb(0) returns -infinity with a division by zero exception.

STANDARDS

The ilogb(), ilogbf(), ilogbl(), logb(), logbf(), and logbl() routines conform to ISO/IEC 9899:1999 (“ISO C99”). The latter three implement the logb function recommended by IEEE Std 754-1985.

HISTORY

Function: First Appeared In
logb(): 4.3BSD
ilogb(): FreeBSD 1.1.5
ilogbf(): FreeBSD 2.0
logbf(): FreeBSD 2.0
ilogbl(): FreeBSD 5.4
logbl(): FreeBSD 8.0