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.TH MATH-FP 2
.SH NAME
math-fp \- floating point
.SH SYNOPSIS
.EX
include "math.m";
math := load Math Math->PATH;
Infinity, NaN, MachEps, Pi, Degree: real;
INVAL, ZDIV, OVFL, UNFL, INEX: int;
RND_NR, RND_NINF, RND_PINF, RND_Z, RND_MASK: int;
getFPcontrol, getFPstatus: fn(): int;
FPcontrol, FPstatus: fn(r, mask: int): int;
ilogb: fn(x: real): int;
scalbn: fn(x: real, n: int): real;
copysign: fn(x, s: real): real;
finite, isnan: fn(x: real): int;
nextafter: fn(x, y: real): real;
fdim, fmin, fmax: fn(x, y: real): real;
fabs: fn(x: real): real;
ceil, floor: fn(x: real): real;
remainder: fn(x, p: real): real;
fmod: fn(x, y: real): real;
modf: fn(x: real): (int,real);
rint: fn(x: real): real;
.EE
.SH DESCRIPTION
These constants and functions provide control over rounding modes,
exceptions, and other properties of floating point arithmetic.
.PP
.B Infinity
and
.B NaN
are constants containing
the positive infinity and quiet not-a-number values
of the IEEE binary floating point standard, double precision.
.B MachEps
is 2\u\s-2-52\s0\d, the smallest
.I e
such that 1+\f2e\f1 is not equal to 1.
.B Pi
is the nearest machine number to the infinitely precise value.
.B Degree
is
.BR Pi/ 180.
.PP
Each thread has a floating point control word (governing rounding mode and
whether a particular floating point exception causes a trap)
and a floating point status word (storing accumulated exception flags).
The functions
.B FPcontrol
and
.B FPstatus
copy bits to the control or status word,
in positions specified by a mask, returning the previous values of the bits
specified in the mask.
The functions
.B getFPcontrol
and
.B getFPstatus
return the words unchanged.
.PP
.BR INVAL ,
.BR ZDIV ,
.BR OVFL ,
.BR UNFL ,
and
.B INEX
are non-overlapping single-bit masks
used to compose arguments or return values.
They stand for the five IEEE exceptions:
`invalid operation' (0/0,0+NaN,Infinity-Infinity,sqrt(-1)),
`division by zero' (1/0), `overflow' (1.8e308), `underflow' (1.1e-308),
and `inexact' (.3*.3).
.PP
.BR RND_NR ,
.BR RND_NINF ,
.BR RND_PINF ,
and
.BR RND_Z
are distinct bit patterns
for `round to nearest even', `round toward negative infinity',
`round toward infinity', and `round toward 0',
any of which can be set or extracted from the floating point control
word using
.BR RND_MASK .
For example,
.B FPcontrol(0,
.B UNFL)
makes underflow silent;
.B FPstatus(0,
.B INEX)
checks and clears the inexact flag; and
.B FPcontrol(RND_PINF,
.B RND_MASK)
sets directed rounding.
.PP
By default,
.B INEX
is quiet,
.BR OVFL ,
.BR UNFL ,
and
.B ZDIV
are fatal,
and rounding is to nearest even.
Limbo modules are
entitled to assume this, and if they wish to use quiet
underflow, overflow, or zero-divide, they must either
set and restore the control register or clearly document that
their caller must do so.
.PP
The
.B ilogb
function
returns the nearest integral logarithm base 2 of the absolute value of
.IR x:
for positive finite
.IR x ,
1 \(<=
.IB x *2\u-\s-2ilogb( x )\s0\d
< 2,
and
.BI ilogb(- x )
.B =
.BI ilogb( x )\f1.
.BI Scalbn( x , n )
is a scaled power of two:
.IB x *2\u\s-2n\s0\d\f1.
.BI Copysign( x , s )
has the magnitude of
.I x
and the
sign bit of
.IR s .
.BI Nextafter( x , y )
is the machine number nearest x closer to y.
Finally,
.BI finite( x )
is 0 if
.I x
is
.B Nan
or
.B Infinity,
1 otherwise, and
.BI isnan( x )
is 1 if
.I x
is
.B Nan
and 0 otherwise.
.PP
The function
.BI fdim( x , y)
=
.IB x - y
if
.I x
is greater than
.IR y ,
otherwise it is 0.
The functions
.BR fmin ,
.BR fmax ,
.BR fabs ,
.BR ceil ,
and
.B floor
are the
customary minimum,
maximum,
absolute value,
and integer rounding routines.
.PP
There are two functions for computing the modulus:
.BI fmod( x , y )
is the function defined by the C standard which gives the value
.IB x - i*y
for some
.I i
such that the remainder has the sign of
.I x
and magnitude less than the magnitude of
.IR y ,
while
.BI remainder( x , y )
is the function defined by the IEEE standard
which gives a remainder of magnitude no more than half the
magnitude of
.IR y .
The function
.BI modf( x )
breaks
.I x
into integer and fractional parts returned in a tuple, and
.B rint
rounds to an integer, following the
rounding mode specified in the floating point control word.
.SH SOURCE
.B /libinterp/math.c
.SH SEE ALSO
.IR math-intro (2)
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