220 lines
8.2 KiB
TeX
220 lines
8.2 KiB
TeX
@node Math
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@chapter Mathematical Functions (@file{math.h})
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This chapter groups a wide variety of mathematical functions. The
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corresponding definitions and declarations are in @file{math.h}.
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Two definitions from @file{math.h} are of particular interest.
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@enumerate
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@item
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The representation of infinity as a @code{double} is defined as
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@code{HUGE_VAL}; this number is returned on overflow by many functions.
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The macro @code{HUGE_VALF} is a corresponding value for @code{float}.
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@item
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The structure @code{exception} is used when you write customized error
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handlers for the mathematical functions. You can customize error
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handling for most of these functions by defining your own version of
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@code{matherr}; see the section on @code{matherr} for details.
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@end enumerate
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@cindex system calls
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@cindex support subroutines
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@cindex stubs
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@cindex OS stubs
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Since the error handling code calls @code{fputs}, the mathematical
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subroutines require stubs or minimal implementations for the same list
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of OS subroutines as @code{fputs}: @code{close}, @code{fstat},
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@code{isatty}, @code{lseek}, @code{read}, @code{sbrk}, @code{write}.
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@xref{syscalls,,System Calls, libc.info, The Red Hat newlib C Library},
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for a discussion and for sample minimal implementations of these support
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subroutines.
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Alternative declarations of the mathematical functions, which exploit
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specific machine capabilities to operate faster---but generally have
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less error checking and may reflect additional limitations on some
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machines---are available when you include @file{fastmath.h} instead of
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@file{math.h}.
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@menu
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* version:: Version of library
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* acos:: Arccosine
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* acosh:: Inverse hyperbolic cosine
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* asin:: Arcsine
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* asinh:: Inverse hyperbolic sine
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* atan:: Arctangent
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* atan2:: Arctangent of y/x
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* atanh:: Inverse hyperbolic tangent
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* jN:: Bessel functions (jN, yN)
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* cbrt:: Cube root
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* copysign:: Sign of Y, magnitude of X
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* cosh:: Hyperbolic cosine
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* erf:: Error function (erf, erfc)
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* exp:: Exponential, base e
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* exp2:: Exponential, base 2
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* expm1:: Exponential, base e, of x - 1
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* fabs:: Absolute value (magnitude)
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* fdim:: Positive difference
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* floor:: Floor and ceiling (floor, ceil)
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* fma:: Floating multiply add
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* fmax:: Maximum
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* fmin:: Minimum
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* fmod:: Floating-point remainder (modulo)
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* fpclassify:: Floating-point classification macro
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* frexp:: Split floating-point number
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* gamma:: Logarithmic gamma function
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* hypot:: Distance from origin
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* ilogb:: Get exponent
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* infinity:: Floating infinity
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* isgreater:: Comparison macros
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* ldexp:: Scale by a power of 2
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* log:: Natural logarithms
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* log10:: Base 10 logarithms
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* log1p:: Log of 1 + X
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* log2:: Base 2 logarithms
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* logb:: Get exponent
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* lrint:: Round to integer
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* lround:: Round to integer, away from zero (lround, llround)
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* matherr:: Modifiable math error handler
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* modf:: Split fractional and integer parts
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* nan:: Floating Not a Number
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* nearbyint:: Round to integer
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* nextafter:: Get next representable number
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* pow:: X to the power Y
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* remainder:: remainder of X divided by Y
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* remquo:: Remainder and part of quotient
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* rint:: Round to integer
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* round:: Round to integer, away from zero
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* scalbn:: Scale by a power of FLT_RADIX (2)
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* signbit:: Does floating-point number have negative sign?
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* sin:: Sine or cosine (sin, cos)
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* sinh:: Hyperbolic sine
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* sqrt:: Positive square root
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* tan:: Tangent
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* tanh:: Hyperbolic tangent
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* trunc:: Round to integer, towards zero
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@end menu
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@page
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@node version
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@section Error Handling
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There are four different versions of the math library routines: IEEE,
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POSIX, X/Open, or SVID. The version may be selected at runtime by
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setting the global variable @code{_LIB_VERSION}, defined in
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@file{math.h}. It may be set to one of the following constants defined
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in @file{math.h}: @code{_IEEE_}, @code{_POSIX_}, @code{_XOPEN_}, or
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@code{_SVID_}. The @code{_LIB_VERSION} variable is not specific to any
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thread, and changing it will affect all threads.
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The versions of the library differ only in how errors are handled.
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In IEEE mode, the @code{matherr} function is never called, no warning
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messages are printed, and @code{errno} is never set.
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In POSIX mode, @code{errno} is set correctly, but the @code{matherr}
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function is never called and no warning messages are printed.
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In X/Open mode, @code{errno} is set correctly, and @code{matherr} is
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called, but warning message are not printed.
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In SVID mode, functions which overflow return 3.40282346638528860e+38,
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the maximum single-precision floating-point value, rather than infinity.
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Also, @code{errno} is set correctly, @code{matherr} is called, and, if
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@code{matherr} returns 0, warning messages are printed for some errors.
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For example, by default @samp{log(-1.0)} writes this message on standard
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error output:
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@example
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log: DOMAIN error
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@end example
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The library is set to X/Open mode by default.
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The aforementioned error reporting is the supported Newlib libm error
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handling method. However, the majority of the functions are written
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so as to produce the floating-point exceptions (e.g. "invalid",
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"divide-by-zero") as required by the C and POSIX standards, for
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floating-point implementations that support them. Newlib does not provide
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the floating-point exception access routines defined in the standards
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for fenv.h, though, which is why they are considered unsupported. It is
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mentioned in case you have separately-provided access routines so that
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you are aware that they can be caused.
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@section Standards Compliance And Portability
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Most of the individual function descriptions describe the standards to which
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each function complies. However, these descriptions are mostly out of date,
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having been written before C99 was released. One of these days we'll get
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around to updating the rest of them. (If you'd like to help, please let us
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know.)
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``C99'' refers to ISO/IEC 9899:1999, ``Programming languages--C''.
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``POSIX'' refers to IEEE Standard 1003.1. POSIX@registeredsymbol{} is a
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registered trademark of The IEEE.
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@c To sort the include list easily, keep the indentation right because want to
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@c skip the s_|w_ at the start of most--but not all--of the file names.
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@c (e.g., isgreater.def does not have a leading s nor w.) Then, sort
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@c based on the column. For example: "sort -t@ -k3.17"
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@c A few hand-edits might be appropriate after a sort, although not necessary
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@c and are a nuisance as ought to be kept in sync with menu list above:
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@c atan2 after atan, exp2 after exp, log first in log list, and w_j0 to place
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@c to reflect function name of Bessel (as opposed to j; e.g. after atanh,
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@c before cbrt).
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@page @include math/w_acos.def
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@page @include math/w_acosh.def
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@page @include math/w_asin.def
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@page @include math/s_asinh.def
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@page @include math/s_atan.def
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@page @include math/w_atan2.def
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@page @include math/w_atanh.def
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@page @include math/w_j0.def
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@page @include common/s_cbrt.def
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@page @include common/s_copysign.def
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@page @include math/w_cosh.def
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@page @include math/s_erf.def
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@page @include math/w_exp.def
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@page @include math/w_exp2.def
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@page @include common/s_expm1.def
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@page @include math/s_fabs.def
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@page @include common/s_fdim.def
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@page @include math/s_floor.def
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@page @include common/s_fma.def
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@page @include common/s_fmax.def
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@page @include common/s_fmin.def
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@page @include math/w_fmod.def
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@page @include math/s_frexp.def
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@page @include math/w_gamma.def
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@page @include math/w_hypot.def
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@page @include common/s_ilogb.def
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@page @include common/s_infinity.def
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@page @include common/isgreater.def
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@page @include common/s_isnan.def
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@page @include math/s_ldexp.def
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@page @include math/w_log.def
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@page @include math/w_log10.def
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@page @include common/s_log1p.def
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@page @include common/s_log2.def
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@page @include common/s_logb.def
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@page @include common/s_lrint.def
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@page @include common/s_lround.def
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@page @include common/s_matherr.def
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@page @include common/s_modf.def
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@page @include common/s_nan.def
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@page @include common/s_nearbyint.def
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@page @include common/s_nextafter.def
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@page @include math/w_pow.def
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@page @include math/w_remainder.def
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@page @include common/s_remquo.def
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@page @include common/s_rint.def
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@page @include common/s_round.def
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@page @include common/s_scalbn.def
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@page @include common/s_signbit.def
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@page @include math/s_sin.def
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@page @include math/w_sinh.def
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@page @include math/w_sqrt.def
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@page @include math/s_tan.def
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@page @include math/s_tanh.def
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@page @include common/s_trunc.def
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