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logb.3p (4331B)

    

  1. '\" et
  2. .TH LOGB "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
  3. .\"
  4. .SH PROLOG
  5. This manual page is part of the POSIX Programmer's Manual.
  6. The Linux implementation of this interface may differ (consult
  7. the corresponding Linux manual page for details of Linux behavior),
  8. or the interface may not be implemented on Linux.
  9. .\"
  10. .SH NAME
  11. logb,
  12. logbf,
  13. logbl
  14. \(em radix-independent exponent
  15. .SH SYNOPSIS
  16. .LP
  17. .nf
  18. #include <math.h>
  19. .P
  20. double logb(double \fIx\fP);
  21. float logbf(float \fIx\fP);
  22. long double logbl(long double \fIx\fP);
  23. .fi
  24. .SH DESCRIPTION
  25. The functionality described on this reference page is aligned with the
  26. ISO\ C standard. Any conflict between the requirements described here and the
  27. ISO\ C standard is unintentional. This volume of POSIX.1\(hy2017 defers to the ISO\ C standard.
  28. .P
  29. These functions shall compute the exponent of
  30. .IR x ,
  31. which is the integral part of log\fI\d\s-3r\s+3\u\fR
  32. |\|\fIx\fR\||, as a signed floating-point value, for non-zero
  33. .IR x ,
  34. where
  35. .IR r
  36. is the radix of the machine's floating-point arithmetic, which is the
  37. value of FLT_RADIX defined in the
  38. .IR <float.h> 
  39. header.
  40. .P
  41. If
  42. .IR x
  43. is subnormal it is treated as though it were normalized; thus for
  44. finite positive
  45. .IR x :
  46. .sp
  47. .RS 4
  48. .nf
  50. 1 <= \fIx\fP * FLT_RADIX\s-3\u-logb(x)\d\s+3 < FLT_RADIX
  51. .fi
  52. .P
  53. .RE
  54. .P
  55. An application wishing to check for error situations should set
  56. .IR errno
  57. to zero and call
  58. .IR feclearexcept (FE_ALL_EXCEPT)
  59. before calling these functions. On return, if
  60. .IR errno
  61. is non-zero or \fIfetestexcept\fR(FE_INVALID | FE_DIVBYZERO |
  62. FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.
  63. .SH "RETURN VALUE"
  64. Upon successful completion, these functions shall return the exponent
  65. of
  66. .IR x .
  67. .P
  68. If
  69. .IR x
  70. is \(+-0,
  71. \fIlogb\fR(),
  72. \fIlogbf\fR(),
  73. and
  74. \fIlogbl\fR()
  75. shall return \-HUGE_VAL, \-HUGE_VALF, and \-HUGE_VALL,
  76. respectively.
  77. .P
  78. On systems that support the IEC 60559 Floating-Point option, a pole
  79. error shall occur;
  80. .br
  81. otherwise, a
  82. pole
  83. error may occur.
  84. .P
  85. If
  86. .IR x
  87. is NaN, a NaN shall be returned.
  88. .P
  89. If
  90. .IR x
  91. is \(+-Inf, +Inf shall be returned.
  92. .SH ERRORS
  93. These functions shall fail if:
  94. .IP "Pole\ Error" 12
  95. The value of
  96. .IR x
  97. is \(+-0.
  98. .RS 12 
  99. .P
  100. If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
  101. non-zero, then
  102. .IR errno
  103. shall be set to
  104. .BR [ERANGE] .
  105. If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
  106. non-zero, then the divide-by-zero floating-point exception shall be
  107. raised.
  108. .RE
  109. .P
  110. These functions may fail if:
  111. .IP "Pole\ Error" 12
  112. The value of
  113. .IR x
  114. is 0.
  115. .RS 12 
  116. .P
  117. If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
  118. non-zero, then
  119. .IR errno
  120. shall be set to
  121. .BR [ERANGE] .
  122. If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
  123. non-zero, then the divide-by-zero floating-point exception shall be
  124. raised.
  125. .RE
  126. .LP
  127. .IR "The following sections are informative."
  128. .SH EXAMPLES
  129. None.
  130. .SH "APPLICATION USAGE"
  131. On error, the expressions (\fImath_errhandling\fR & MATH_ERRNO) and
  132. (\fImath_errhandling\fR & MATH_ERREXCEPT) are independent of each
  133. other, but at least one of them must be non-zero.
  134. .SH RATIONALE
  135. None.
  136. .SH "FUTURE DIRECTIONS"
  137. None.
  138. .SH "SEE ALSO"
  139. .IR "\fIfeclearexcept\fR\^(\|)",
  140. .IR "\fIfetestexcept\fR\^(\|)",
  141. .IR "\fIilogb\fR\^(\|)",
  142. .IR "\fIscalbln\fR\^(\|)"
  143. .P
  144. The Base Definitions volume of POSIX.1\(hy2017,
  145. .IR "Section 4.20" ", " "Treatment of Error Conditions for Mathematical Functions",
  146. .IR "\fB<float.h>\fP",
  147. .IR "\fB<math.h>\fP"
  148. .\"
  149. .SH COPYRIGHT
  150. Portions of this text are reprinted and reproduced in electronic form
  151. from IEEE Std 1003.1-2017, Standard for Information Technology
  152. -- Portable Operating System Interface (POSIX), The Open Group Base
  153. Specifications Issue 7, 2018 Edition,
  154. Copyright (C) 2018 by the Institute of
  155. Electrical and Electronics Engineers, Inc and The Open Group.
  156. In the event of any discrepancy between this version and the original IEEE and
  157. The Open Group Standard, the original IEEE and The Open Group Standard
  158. is the referee document. The original Standard can be obtained online at
  159. http://www.opengroup.org/unix/online.html .
  160. .PP
  161. Any typographical or formatting errors that appear
  162. in this page are most likely
  163. to have been introduced during the conversion of the source files to
  164. man page format. To report such errors, see
  165. https://www.kernel.org/doc/man-pages/reporting_bugs.html .