std::ldexp,std::ldexpf,std::ldexpl(3)

NAME
std::ldexp,std::ldexpf,std::ldexpl - std::ldexp,std::ldexpf,std::ldexpl

Synopsis
   Defined in header <cmath>
   float ldexp ( float x, int exp ); (1) (constexpr since C++23)
   float ldexpf( float x, int exp ); (2) (since C++11)
                        (constexpr since C++23)
   double ldexp ( double x, int exp ); (3) (constexpr since C++23)
   long double ldexp ( long double x, int exp ); (4) (constexpr since C++23)
   long double ldexpl( long double x, int exp ); (5) (since C++11)
                        (constexpr since C++23)
   double ldexp ( IntegralType x, int exp ); (6) (since C++11)
                        (constexpr since C++23)
   1-5) Multiplies a floating point value x by the number 2 raised to the exp power.
   6) A set of overloads or a function template accepting an argument of any integral
   type. Equivalent to (3) (the argument is cast to double).

Parameters
   x - floating point value
   exp - integer value

Return value
   If no errors occur, x multiplied by 2 to the power of exp (x×2exp
   ) 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.

Error handling
   Errors are reported as specified in math_errhandling.
   If the implementation supports IEEE floating-point arithmetic (IEC 60559),
     * Unless a range error occurs, FE_INEXACT is never raised (the result is exact)
     * Unless a range error occurs, the current rounding mode is ignored
     * If x is ±0, it is returned, unmodified
     * If x is ±∞, it is returned, unmodified
     * If exp is 0, then x is returned, unmodified
     * If x is NaN, NaN is returned

Notes
   On binary systems (where FLT_RADIX is 2), std::ldexp is equivalent to std::scalbn.
   The function std::ldexp ("load exponent"), together with its dual, std::frexp, can
   be used to manipulate the representation of a floating-point number without direct
   bit manipulations.
   On many implementations, std::ldexp is less efficient than multiplication or
   division by a power of two using arithmetic operators.

Example
// Run this code
 #include <iostream>
 #include <cmath>
 #include <cerrno>
 #include <cstring>
 #include <cfenv>
 // #pragma STDC FENV_ACCESS ON
 int main()
 {
     std::cout << "ldexp(7, -4) = " << std::ldexp(7, -4) << '\n'
               << "ldexp(1, -1074) = " << std::ldexp(1, -1074)
               << " (minimum positive subnormal double)\n"
               << "ldexp(nextafter(1,0), 1024) = "
               << std::ldexp(std::nextafter(1,0), 1024)
               << " (largest finite double)\n";
     // special values
     std::cout << "ldexp(-0, 10) = " << std::ldexp(-0.0, 10) << '\n'
               << "ldexp(-Inf, -1) = " << std::ldexp(-INFINITY, -1) << '\n';
     // error handling
     errno = 0;
     std::feclearexcept(FE_ALL_EXCEPT);
     std::cout << "ldexp(1, 1024) = " << std::ldexp(1, 1024) << '\n';
     if (errno == ERANGE)
         std::cout << " errno == ERANGE: " << std::strerror(errno) << '\n';
     if (std::fetestexcept(FE_OVERFLOW))
         std::cout << " FE_OVERFLOW raised\n";
 }

Output:
 ldexp(7, -4) = 0.4375
 ldexp(1, -1074) = 4.94066e-324 (minimum positive subnormal double)
 ldexp(nextafter(1,0), 1024) = 1.79769e+308 (largest finite double)
 ldexp(-0, 10) = -0
 ldexp(-Inf, -1) = -inf
 ldexp(1, 1024) = inf
     errno == ERANGE: Numerical result out of range
     FE_OVERFLOW raised

See also
   frexp
   frexpf decomposes a number into significand and a power of 2
   frexpl (function)
   (C++11)
   (C++11)
   scalbn
   scalbnf
   scalbnl
   scalbln
   scalblnf
   scalblnl multiplies a number by FLT_RADIX raised to a power
   (C++11) (function)
   (C++11)
   (C++11)
   (C++11)
   (C++11)
   (C++11)