man3/ldexp.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
   3 .\"     <mtk.manpages@gmail.com>
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  27 .\" References consulted:
  28 .\"     Linux libc source code
  29 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  30 .\"     386BSD man pages
  31 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  32 .\" Modified 2004-10-31 by aeb
  33 .\"
  34 .TH LDEXP 3 2017-09-15 "" "Linux Programmer's Manual"
  35 .SH NAME
  36 ldexp, ldexpf, ldexpl \- multiply floating-point number by integral power of 2
  37 .SH SYNOPSIS
  38 .nf
  39 .B #include <math.h>
  40 .PP
  41 .BI "double ldexp(double " x ", int " exp );
  42 .BI "float ldexpf(float " x ", int " exp );
  43 .BI "long double ldexpl(long double " x ", int " exp );
  44 .fi
  45 .PP
  46 Link with \fI\-lm\fP.
  47 .PP
  48 .in -4n
  49 Feature Test Macro Requirements for glibc (see
  50 .BR feature_test_macros (7)):
  51 .in
  52 .PP
  53 .ad l
  54 .BR ldexpf (),
  55 .BR ldexpl ():
  56 .RS 4
  57 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  58     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  59     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  60 .RE
  61 .ad
  62 .SH DESCRIPTION
  63 These functions return the result of multiplying the floating-point number
  64 .I x
  65 by 2 raised to the power
  66 .IR exp .
  67 .SH RETURN VALUE
  68 On success, these functions return
  69 .IR "x * (2^exp)" .
  70 .PP
  71 If
  72 .I exp
  73 is zero, then
  74 .I x
  75 is returned.
  76 .PP
  77 If
  78 .I x
  79 is a NaN,
  80 a NaN is returned.
  81 .PP
  82 If
  83 .I x
  84 is positive infinity (negative infinity),
  85 positive infinity (negative infinity) is returned.
  86 .PP
  87 If the result underflows,
  88 a range error occurs,
  89 and zero is returned.
  90 .PP
  91 If the result overflows,
  92 a range error occurs,
  93 and the functions return
  94 .BR HUGE_VAL ,
  95 .BR HUGE_VALF ,
  96 or
  97 .BR HUGE_VALL ,
  98 respectively, with a sign the same as
  99 .IR x .
 100 .SH ERRORS
 101 See
 102 .BR math_error (7)
 103 for information on how to determine whether an error has occurred
 104 when calling these functions.
 105 .PP
 106 The following errors can occur:
 107 .TP
 108 Range error, overflow
 109 .I errno
 110 is set to
 111 .BR ERANGE .
 112 An overflow floating-point exception
 113 .RB ( FE_OVERFLOW )
 114 is raised.
 115 .TP
 116 Range error, underflow
 117 .I errno
 118 is set to
 119 .BR ERANGE .
 120 An underflow floating-point exception
 121 .RB ( FE_UNDERFLOW )
 122 is raised.
 123 .SH ATTRIBUTES
 124 For an explanation of the terms used in this section, see
 125 .BR attributes (7).
 126 .TS
 127 allbox;
 128 lbw27 lb lb
 129 l l l.
 130 Interface       Attribute       Value
 131 T{
 132 .BR ldexp (),
 133 .BR ldexpf (),
 134 .BR ldexpl ()
 135 T}      Thread safety   MT-Safe
 136 .TE
 137 .SH CONFORMING TO
 138 C99, POSIX.1-2001, POSIX.1-2008.
 139 .PP
 140 The variant returning
 141 .I double
 142 also conforms to
 143 SVr4, 4.3BSD, C89.
 144 .SH SEE ALSO
 145 .BR frexp (3),
 146 .BR modf (3),
 147 .BR scalbln (3)