#define scalbn( arg, exp )
(4) (since C99) float scalblnf( float arg, long exp ); (5) (since C99) double scalbln( double arg, long exp ); (6) (since C99) long double scalblnl( long double arg, long exp ); (7) (since C99)#define scalbln( arg, exp )
(8) (since C99) 1-3,5-7)Multiplies a floating-point value
argby
FLT_RADIXraised to power
exp.
4,8) Type-generic macros: If arg has type long double, scalbnl or scalblnl is called. Otherwise, if arg has integer type or the type double, scalbn or scalbln is called. Otherwise, scalbnf or scalblnf is called, respectively.
If no errors occur, arg multiplied by FLT_RADIX to the power of exp (arg×FLT_RADIXexp
) is returned.
If a range error due to overflow occurs, ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL is returned.
If a range error due to underflow occurs, the correct result (after rounding) is returned.
[edit] Error handlingErrors are reported as specified in math_errhandling.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
arg is returned, unmodified.On binary systems (where FLT_RADIX is 2), scalbn is equivalent to ldexp.
Although scalbn and scalbln are specified to perform the operation efficiently, on many implementations they are less efficient than multiplication or division by a power of two using arithmetic operators.
The scalbln function is provided because the factor required to scale from the smallest positive floating-point value to the largest finite one may be greater than 32767, the standard-guaranteed INT_MAX. In particular, for the 80-bit long double, the factor is 32828.
#include <errno.h>
#include <fenv.h>
#include <float.h>
#include <math.h>
#include <stdio.h>
// #pragma STDC FENV_ACCESS ON
int main(void)
{
printf("scalbn(7, -4) = %f\n", scalbn(7, -4));
printf("scalbn(1, -1074) = %g (minimum positive subnormal double)\n",
scalbn(1, -1074));
printf("scalbn(nextafter(1,0), 1024) = %g (largest finite double)\n",
scalbn(nextafter(1,0), 1024));
// special values
printf("scalbn(-0, 10) = %f\n", scalbn(-0.0, 10));
printf("scalbn(-Inf, -1) = %f\n", scalbn(-INFINITY, -1));
// error handling
errno = 0; feclearexcept(FE_ALL_EXCEPT);
printf("scalbn(1, 1024) = %f\n", scalbn(1, 1024));
if (errno == ERANGE)
perror(" errno == ERANGE");
if (fetestexcept(FE_OVERFLOW))
puts(" FE_OVERFLOW raised");
}
Possible output:
scalbn(7, -4) = 0.437500
scalbn(1, -1074) = 4.94066e-324 (minimum positive subnormal double)
scalbn(nextafter(1,0), 1024) = 1.79769e+308 (largest finite double)
scalbn(-0, 10) = -0.000000
scalbn(-Inf, -1) = -inf
scalbn(1, 1024) = inf
errno == ERANGE: Numerical result out of range
FE_OVERFLOW raised[edit] References
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