1log2(3M)                Mathematical Library Functions                log2(3M)
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NAME

6       log2, log2f, log2l - compute base 2 logarithm functions
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SYNOPSIS

9       c99 [ flag... ] file... -lm [ library... ]
10       #include <math.h>
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12       double log2(double x);
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15       float log2f(float x);
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18       long double log2l(long double x);
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DESCRIPTION

22       These  functions  compute  the  base  2  logarithm of their argument x,
23       log2(x).
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RETURN VALUES

26       Upon successful completion, these functions return the base 2 logarithm
27       of x.
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30       If x is ±0, a pole error occurs and log2(), log2f(), and log2l() return
31HUGE_VAL, −HUGE_VALF, and −HUGE_VALL, respectively.
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34       For finite values of x that are less than 0,  or if x is −Inf a  domain
35       error occurs and a NaN is returned.
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38       If x is NaN, a NaN is returned.
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41       If x is 1, +0 is returned.
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44       If x is +Inf, x is returned.
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ERRORS

47       These functions will fail if:
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49       Domain Error    The finite value of x is less than 0, or x is −Inf.
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51                       If   the   integer   expression   (math_errhandling   &
52                       MATH_ERREXCEPT) is non-zero, then the invalid floating-
53                       point exception is raised.
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56       Pole Error      The value of x is 0.
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58                       If   the   integer   expression   (math_errhandling   &
59                       MATH_ERREXCEPT) is non-zero,  then  the  divide-by-zero
60                       floating-point exception is raised.
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USAGE

64       An  application  wanting to check for exceptions should call feclearex‐
65       cept(FE_ALL_EXCEPT) before  calling  these  functions.  On  return,  if
66       fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is
67       non-zero, an exception has been raised. An  application  should  either
68       examine the return value or check the floating point exception flags to
69       detect exceptions.
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ATTRIBUTES

72       See attributes(5) for descriptions of the following attributes:
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77       ┌─────────────────────────────┬─────────────────────────────┐
78       │      ATTRIBUTE TYPE         │      ATTRIBUTE VALUE        │
79       ├─────────────────────────────┼─────────────────────────────┤
80       │Interface Stability          │Standard                     │
81       ├─────────────────────────────┼─────────────────────────────┤
82       │MT-Level                     │MT-Safe                      │
83       └─────────────────────────────┴─────────────────────────────┘
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SEE ALSO

86       feclearexcept(3M),    fetestexcept(3M),     log(3M),     math.h(3HEAD),
87       attributes(5), standards(5)
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91SunOS 5.11                        12 Jul 2006                         log2(3M)
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