1LOGB(3P) POSIX Programmer's Manual LOGB(3P)
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6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
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12 logb, logbf, logbl - radix-independent exponent
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15 #include <math.h>
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17 double logb(double x);
18 float logbf(float x);
19 long double logbl(long double x);
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23 These functions shall compute the exponent of x, which is the integral
24 part of log_r |x|, as a signed floating-point value, for non-zero x,
25 where r is the radix of the machine's floating-point arithmetic, which
26 is the value of FLT_RADIX defined in the <float.h> header.
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28 If x is subnormal it is treated as though it were normalized; thus for
29 finite positive x:
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32 1 <= x * FLT_RADIX**-logb(x) < FLT_RADIX
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34 An application wishing to check for error situations should set errno
35 to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these
36 functions. On return, if errno is non-zero or fetestexcept(FE_INVALID
37 | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
38 occurred.
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41 Upon successful completion, these functions shall return the exponent
42 of x.
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44 If x is ±0, a pole error shall occur and logb(), logbf(), and logbl()
45 shall return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively.
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47 If x is NaN, a NaN shall be returned.
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49 If x is ±Inf, +Inf shall be returned.
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52 These functions shall fail if:
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54 Pole Error
55 The value of x is ±0.
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57 If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
58 then errno shall be set to [ERANGE]. If the integer expression
59 (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-
60 zero floating-point exception shall be raised.
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63 The following sections are informative.
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66 None.
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69 On error, the expressions (math_errhandling & MATH_ERRNO) and
70 (math_errhandling & MATH_ERREXCEPT) are independent of each other, but
71 at least one of them must be non-zero.
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74 None.
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77 None.
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80 feclearexcept(), fetestexcept(), ilogb(), scalb(), the Base Definitions
81 volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Condi‐
82 tions for Mathematical Functions, <float.h>, <math.h>
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85 Portions of this text are reprinted and reproduced in electronic form
86 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
87 -- Portable Operating System Interface (POSIX), The Open Group Base
88 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
89 Electrical and Electronics Engineers, Inc and The Open Group. In the
90 event of any discrepancy between this version and the original IEEE and
91 The Open Group Standard, the original IEEE and The Open Group Standard
92 is the referee document. The original Standard can be obtained online
93 at http://www.opengroup.org/unix/online.html .
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97IEEE/The Open Group 2003 LOGB(3P)