log1p
, log1pf
, log1pl
Computes the natural logarithm of 1 plus the specified value.
Syntax
double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);
#define log1p(X) // Requires C11 or higher
float log1p(float x); //C++ only
long double log1p(long double x); //C++ only
Parameters
x
The floating-point argument.
Return value
If successful, returns the natural (base-e) log of (x
+ 1).
Otherwise, may return one of the following values:
Input | Result | SEH exception | errno |
---|---|---|---|
+INF | +INF | ||
Denormals | Same as input | UNDERFLOW |
|
±0 | Same as input | ||
-1 | -INF | DIVBYZERO |
ERANGE |
< -1 | NaN | INVALID |
EDOM |
-INF | NaN | INVALID |
EDOM |
±SNaN | Same as input | INVALID |
|
±QNaN, indefinite | Same as input |
The errno
value is set to ERANGE if x
= -1. The errno
value is set to EDOM
if x
< -1.
Remarks
The log1p
functions may be more accurate than using log(x + 1)
when x
is near 0.
Because C++ allows overloading, you can call overloads of log1p
that take and return float
and long double
types. In a C program, unless you're using the <tgmath.h> macro to call this function, log1p
always takes and returns a double
.
If you use the <tgmath.h>
log1p()
macro, the type of the argument determines which version of the function is selected. See Type-generic math for details.
Where x
is a natural number, this function returns the base e logarithm of x
+ 1.
By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.
Requirements
Function | C header | C++ header |
---|---|---|
log1p , log1pf , log1pl |
<math.h> |
<cmath> |
log1p macro |
<tgmath.h> |
For more compatibility information, see Compatibility.
See also
Alphabetical function reference
log2
, log2f
, log2l
log
, logf
, log10
, log10f
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