Defined in header <math.h> | ||
---|---|---|
float ldexpf( float arg, int exp ); | (1) | (since C99) |
double ldexp( double arg, int exp ); | (2) | |
long double ldexpl( long double arg, int exp ); | (3) | (since C99) |
Defined in header <tgmath.h> | ||
#define ldexp( arg, exp ) | (4) | (since C99) |
arg
by the number 2 raised to the exp
power.arg
has type long double
, ldexpl
is called. Otherwise, if arg
has integer type or the type double
, ldexp
is called. Otherwise, ldexpf
is called, respectively.Parameters
arg | - | floating point value |
exp | - | integer value |
Return value
If no errors occur, arg
multiplied by 2 to the power of exp
(arg×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
arg
is ±0, it is returned, unmodified - If
arg
is ±∞, it is returned, unmodified - If
exp
is 0, thenarg
is returned, unmodified - If
arg
is NaN, NaN is returned
Notes
On binary systems (where FLT_RADIX
is 2
), ldexp
is equivalent to scalbn
.
The function ldexp
("load exponent"), together with its dual, frexp
, can be used to manipulate the representation of a floating-point number without direct bit manipulations.
On many implementations, ldexp
is less efficient than multiplication or division by a power of two using arithmetic operators.
Example
#include <stdio.h> #include <math.h> #include <float.h> #include <errno.h> #include <fenv.h> #pragma STDC FENV_ACCESS ON int main(void) { printf("ldexp(7, -4) = %f\n", ldexp(7, -4)); printf("ldexp(1, -1074) = %g (minimum positive subnormal double)\n", ldexp(1, -1074)); printf("ldexp(nextafter(1,0), 1024) = %g (largest finite double)\n", ldexp(nextafter(1,0), 1024)); // special values printf("ldexp(-0, 10) = %f\n", ldexp(-0.0, 10)); printf("ldexp(-Inf, -1) = %f\n", ldexp(-INFINITY, -1)); //error handling errno = 0; feclearexcept(FE_ALL_EXCEPT); printf("ldexp(1, 1024) = %f\n", ldexp(1, 1024)); if(errno == ERANGE) perror(" errno == ERANGE"); if(fetestexcept(FE_OVERFLOW)) puts(" FE_OVERFLOW raised"); }
Possible output:
ldexp(7, -4) = 0.437500 ldexp(1, -1074) = 4.94066e-324 (minimum positive subnormal double) ldexp(nextafter(1,0), 1024) = 1.79769e+308 (largest finite double) ldexp(-0, 10) = -0.000000 ldexp(-Inf, -1) = -inf ldexp(1, 1024) = inf errno == ERANGE: Numerical result out of range FE_OVERFLOW raised
References
- C11 standard (ISO/IEC 9899:2011):
- 7.12.6.6 The ldexp functions (p: 244)
- 7.25 Type-generic math <tgmath.h> (p: 373-375)
- F.10.3.6 The ldexp functions (p: 522)
- C99 standard (ISO/IEC 9899:1999):
- 7.12.6.6 The ldexp functions (p: 225)
- 7.22 Type-generic math <tgmath.h> (p: 335-337)
- F.9.3.6 The ldexp functions (p: 459)
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.5.4.3 The ldexp function
See also
(C99)(C99) | breaks a number into significand and a power of 2 (function) |
(C99)(C99)(C99)(C99)(C99)(C99) | computes efficiently a number times FLT_RADIX raised to a power (function) |
C++ documentation for ldexp |
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