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>
   4 .\"
   5 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   6 .\"
   7 .\" References consulted:
   8 .\"     Linux libc source code
   9 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  10 .\"     386BSD man pages
  11 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  12 .\" Modified 2004-10-31 by aeb
  13 .\"
  14 .TH LDEXP 3 2021-03-22 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
  15 .SH NAME
  16 ldexp, ldexpf, ldexpl \- multiply floating-point number by integral power of 2
  17 .SH LIBRARY
  18 Math library
  19 .RI ( libm ", " \-lm )
  20 .SH SYNOPSIS
  21 .nf
  22 .B #include <math.h>
  23 .PP
  24 .BI "double ldexp(double " x ", int " exp );
  25 .BI "float ldexpf(float " x ", int " exp );
  26 .BI "long double ldexpl(long double " x ", int " exp );
  27 .fi
  28 .PP
  29 .RS -4
  30 Feature Test Macro Requirements for glibc (see
  31 .BR feature_test_macros (7)):
  32 .RE
  33 .PP
  34 .BR ldexpf (),
  35 .BR ldexpl ():
  36 .nf
  37     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
  38         || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  39         || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  40 .fi
  41 .SH DESCRIPTION
  42 These functions return the result of multiplying the floating-point number
  43 .I x
  44 by 2 raised to the power
  45 .IR exp .
  46 .SH RETURN VALUE
  47 On success, these functions return
  48 .IR "x * (2^exp)" .
  49 .PP
  50 If
  51 .I exp
  52 is zero, then
  53 .I x
  54 is returned.
  55 .PP
  56 If
  57 .I x
  58 is a NaN,
  59 a NaN is returned.
  60 .PP
  61 If
  62 .I x
  63 is positive infinity (negative infinity),
  64 positive infinity (negative infinity) is returned.
  65 .PP
  66 If the result underflows,
  67 a range error occurs,
  68 and zero is returned.
  69 .PP
  70 If the result overflows,
  71 a range error occurs,
  72 and the functions return
  73 .BR HUGE_VAL ,
  74 .BR HUGE_VALF ,
  75 or
  76 .BR HUGE_VALL ,
  77 respectively, with a sign the same as
  78 .IR x .
  79 .SH ERRORS
  80 See
  81 .BR math_error (7)
  82 for information on how to determine whether an error has occurred
  83 when calling these functions.
  84 .PP
  85 The following errors can occur:
  86 .TP
  87 Range error, overflow
  88 .I errno
  89 is set to
  90 .BR ERANGE .
  91 An overflow floating-point exception
  92 .RB ( FE_OVERFLOW )
  93 is raised.
  94 .TP
  95 Range error, underflow
  96 .I errno
  97 is set to
  98 .BR ERANGE .
  99 An underflow floating-point exception
 100 .RB ( FE_UNDERFLOW )
 101 is raised.
 102 .SH ATTRIBUTES
 103 For an explanation of the terms used in this section, see
 104 .BR attributes (7).
 105 .ad l
 106 .nh
 107 .TS
 108 allbox;
 109 lbx lb lb
 110 l l l.
 111 Interface       Attribute       Value
 112 T{
 113 .BR ldexp (),
 114 .BR ldexpf (),
 115 .BR ldexpl ()
 116 T}      Thread safety   MT-Safe
 117 .TE
 118 .hy
 119 .ad
 120 .sp 1
 121 .SH STANDARDS
 122 C99, POSIX.1-2001, POSIX.1-2008.
 123 .PP
 124 The variant returning
 125 .I double
 126 also conforms to
 127 SVr4, 4.3BSD, C89.
 128 .SH SEE ALSO
 129 .BR frexp (3),
 130 .BR modf (3),
 131 .BR scalbln (3)