log(3m) - osol9

1log(3M)                 Mathematical Library Functions                 log(3M)
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NAME

6       log, logf, logl - natural logarithm function
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SYNOPSIS

9       c99 [ flag... ] file... -lm [ library... ]
10       #include <math.h>
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12       double log(double x);
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15       float logf(float x);
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18       long double logl(long double x);
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DESCRIPTION

22       These  functions  compute  the  natural  logarithm of their argument x,
23       log(e)(x).
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RETURN VALUES

26       Upon successful completion, log() returns the natural logarithm of x.
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29       If x is ±0, a pole error occurs and log(), logf(),  and  logl()  return
30       −HUGE_VAL, −HUGE_VALF, and −HUGE_VALL, respectively.
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33       For  finite values of x that are less than 0, or if x is −Inf, a domain
34       error occurs and a NaN is returned.
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37       If x is NaN, a NaN is returned.
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40       If x is 1, +0 is returned.
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43       If x is +Inf, x is returned.
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46       For exceptional cases, matherr(3M) tabulates the values to be  returned
47       by log() as specified by SVID3 and XPG3.
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ERRORS

50       These functions will fail if:
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52       Domain Error    The finite value of x is negative, or x is -Inf.
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54                       If   the   integer   expression   (math_errhandling   &
55                       MATH_ERREXCEPT) is non-zero, the invalid floating-point
56                       exception is raised.
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58                       The log() function sets errno to EDOM if the value of x
59                       is negative.
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62       Pole Error      The value of x is 0.
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64                       If   the   integer   expression   (math_errhandling   &
65                       MATH_ERREXCEPT)  is non-zero, the divide-by-zero float‐
66                       ing-point exception is raised.
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USAGE

70       An application wanting to check for exceptions should  call  feclearex‐
71       cept(FE_ALL_EXCEPT)  before  calling  these  functions.  On  return, if
72       fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is
73       non-zero,  an  exception  has been raised. An application should either
74       examine the return value or check the floating point exception flags to
75       detect exceptions.
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78       An application can also set errno to 0 before calling log(). On return,
79       if errno is non-zero, an error has  occurred.  The  logf()  and  logl()
80       functions do not set errno.
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ATTRIBUTES

83       See attributes(5) for descriptions of the following attributes:
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88       ┌─────────────────────────────┬─────────────────────────────┐
89       │      ATTRIBUTE TYPE         │      ATTRIBUTE VALUE        │
90       ├─────────────────────────────┼─────────────────────────────┤
91       │Interface Stability          │Standard                     │
92       ├─────────────────────────────┼─────────────────────────────┤
93       │MT-Level                     │MT-Safe                      │
94       └─────────────────────────────┴─────────────────────────────┘
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