logbl(3m) - osol9

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

6       logb, logbf, logbl - radix-independent exponent
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SYNOPSIS

9       c99 [ flag... ] file... -lm [ library... ]
10       #include <math.h>
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12       double logb(double x);
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15       float logbf(float x);
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18       long double logbl(long double x);
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21       cc [ flag... ] file... -lm [ library... ]
22       #include <math.h>
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24       double logb(double x);
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27       float logbf(float x);
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30       long double logbl(long double x);
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DESCRIPTION

34       These  functions  compute the exponent of x, which is the integral part
35       of log(r) |x|, as a signed floating point value, for non-zero x,  where
36       r is the radix of the machine's floating-point arithmetic, which is the
37       value of FLT_RADIX defined in the <float.h> header.
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RETURN VALUES

40       Upon successful completion, these functions return the exponent of x.
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43       If x is subnormal:
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45           o      For SUSv3-conforming applications compiled with the c99 com‐
46                  piler  driver  (see standards(5)), the exponent of x as if x
47                  were normalized is returned.
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49           o      Otherwise, if compiled with the cc compiler  driver,  −1022,
50                  −126,  and  −16382  are  returned  for  logb(), logbf(), and
51                  logbl(), respectively.
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54       If x is ±0, a pole error occurs and logb(), logbf(), and logbl() return
55       −HUGE_VAL, −HUGE_VALF, and −HUGE_VALL, respectively.
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58       If x is NaN, a NaN is returned.
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61       If x is ±Inf, +Inf is returned.
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ERRORS

64       These functions will fail if:
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66       Pole Error    The value of x is ±0.
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68                     If the integer expression (math_errhandling & MATH_ERREX‐
69                     CEPT)  is  non-zero,  the  divide-by-zero  floating-point
70                     exception is raised.
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72                     The  logb() function sets errno to EDOM if the value of x
73                     is 0.
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USAGE

77       An application wanting to check for exceptions should  call  feclearex‐
78       cept(FE_ALL_EXCEPT)  before  calling  these  functions.  On  return, if
79       fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is
80       non-zero,  an  exception  has been raised. An application should either
81       examine the return value or check the floating point exception flags to
82       detect exceptions.
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85       An  application  can  also  set  errno  to  0 before calling logb(). On
86       return, if errno is non-zero, an error has occurred.  The  logbf()  and
87       logbl() functions do not set errno.
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ATTRIBUTES

90       See attributes(5) for descriptions of the following attributes:
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95       ┌─────────────────────────────┬─────────────────────────────┐
96       │      ATTRIBUTE TYPE         │      ATTRIBUTE VALUE        │
97       ├─────────────────────────────┼─────────────────────────────┤
98       │Interface Stability          │Standard                     │
99       ├─────────────────────────────┼─────────────────────────────┤
100       │MT-Level                     │MT-Safe                      │
101       └─────────────────────────────┴─────────────────────────────┘
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