ldexp, ldexpf, ldexpl
| 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
argis ±0, it is returned, unmodified - If
argis ±∞, it is returned, unmodified - If
expis 0, thenargis returned, unmodified - If
argis 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 raisedReferences
- 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
| |