scalb, scalbf, scalbl — multiply floating-point number by integral power of radix (OBSOLETE)


#include <math.h>
double scalb( double x,
  double exp);
float scalbf( float x,
  float exp);
long double scalbl( long double x,
  long double exp);
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_XOPEN_SOURCE >= 500 || /* Since glibc 2.19:
*/ _DEFAULT_SOURCE || /* Glibc versions <= 2.19:
scalbf(), scalbl():
_XOPEN_SOURCE >= 600 || /* Since glibc 2.19:
*/ _DEFAULT_SOURCE || /* Glibc versions <= 2.19:
[Note] Note

Link with −lm.


These functions multiply their first argument x by FLT_RADIX (probably 2) to the power of exp, that is:

    x * FLT_RADIX ** exp

The definition of FLT_RADIX can be obtained by including <float.h>


On success, these functions return x * FLT_RADIX ** exp.

If x or exp is a NaN, a NaN is returned.

If x is positive infinity (negative infinity), and exp is not negative infinity, positive infinity (negative infinity) is returned.

If x is +0 (−0), and exp is not positive infinity, +0 (−0) is returned.

If x is zero, and exp is positive infinity, a domain error occurs, and a NaN is returned.

If x is an infinity, and exp is negative infinity, a domain error occurs, and a NaN is returned.

If the result overflows, a range error occurs, and the functions return HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with a sign the same as x.

If the result underflows, a range error occurs, and the functions return zero, with a sign the same as x.


See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

Domain error: x is 0, and exp is positive infinity, or x is positive infinity and exp is negative infinity and the other argument is not a NaN

An invalid floating-point exception (FE_INVALID) is raised.

Range error, overflow

An overflow floating-point exception (FE_OVERFLOW) is raised.

Range error, underflow

An underflow floating-point exception (FE_UNDERFLOW) is raised.

These functions do not set errno.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
scalb(), scalbf(), scalbl() Thread safety MT-Safe


scalb() is specified in POSIX.1-2001, but marked obsolescent. POSIX.1-2008 removes the specification of scalb(), recommending the use of scalbln(3), scalblnf(3), or scalblnl(3) instead. The scalb() function is from 4.3BSD.

scalbf() and scalbl() are unstandardized; scalbf() is nevertheless present on several other systems


ldexp(3), scalbln(3)


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  Copyright 2004 Andries Brouwer <>.
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