LOG2(3M) | Mathematical Library Functions | LOG2(3M) |

log2, log2f, log2l - compute base 2 logarithm functions

c99 [flag... ]file...-lm[library... ] #include <math.h>doublelog2(doublex);

floatlog2f(floatx);

long doublelog2l(long doublex);

These functions compute the base 2 logarithm of their argument
*x*, **log2**(*x*).

Upon successful completion, these functions return the base 2
logarithm of *x*.

If *x* is ±0, a pole error occurs and **log2()**,
**log2f()**, and **log2l()** return −**HUGE_VAL**,
−**HUGE_VALF**, and −**HUGE_VALL**, respectively.

For finite values of *x* that are less than 0, or if *x*
is −Inf a domain error occurs and a NaN is returned.

If *x* is NaN, a NaN is returned.

If *x* is 1, +0 is returned.

If *x* is +Inf, *x* is returned.

These functions will fail if:

**Domain Error**

The finite value of *x* is less than 0, or *x*
is −Inf.

If the integer expression (**math_errhandling** &
**MATH_ERREXCEPT**) is non-zero, then the invalid floating-point
exception is raised.

**Pole Error**

The value of *x* is 0.

If the integer expression (**math_errhandling** &
**MATH_ERREXCEPT**) is non-zero, then the divide-by-zero floating-point
exception is raised.

An application wanting to check for exceptions should call
**feclearexcept**(**FE_ALL_EXCEPT**) before calling these functions.
On return, if **fetestexcept**(**FE_INVALID** | **FE_DIVBYZERO** |
**FE_OVERFLOW** | **FE_UNDERFLOW**) is non-zero, an exception has been
raised. An application should either examine the return value or check the
floating point exception flags to detect exceptions.

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE | ATTRIBUTE VALUE |

Interface Stability | Standard |

MT-Level | MT-Safe |

math.h(3HEAD), feclearexcept(3M), fetestexcept(3M), log(3M), attributes(7), standards(7)

July 12, 2006 | SunOS 5.11 |