+acos sin.3m inverse trigonometric function 3
+acosh asinh.3m inverse hyperbolic function 3
+asin sin.3m inverse trigonometric function 3
+asinh asinh.3m inverse hyperbolic function 3
+atan sin.3m inverse trigonometric function 1
+atanh asinh.3m inverse hyperbolic function 3
+atan2 sin.3m inverse trigonometric function 2
+cabs hypot.3m complex absolute value 1
+cbrt sqrt.3m cube root 1
+ceil floor.3m integer no less than 0
+copysign ieee.3m copy sign bit 0
+cos sin.3m trigonometric function 1
+cosh sinh.3m hyperbolic function 3
+drem ieee.3m remainder 0
+erf erf.3m error function ???
+erfc erf.3m complementary error function ???
+exp exp.3m exponential 1
+expm1 exp.3m exp(x)\-1 1
+fabs floor.3m absolute value 0
+floor floor.3m integer no greater than 0
+hypot hypot.3m Euclidean distance 1
+infnan infnan.3m signals exceptions
+j0 j0.3m bessel function ???
+j1 j0.3m bessel function ???
+jn j0.3m bessel function ???
+lgamma lgamma.3m log gamma function; (formerly gamma.3m)
+log exp.3m natural logarithm 1
+logb ieee.3m exponent extraction 0
+log10 exp.3m logarithm to base 10 3
+log1p exp.3m log(1+x) 1
+pow exp.3m exponential x**y 60\-500
+rint floor.3m round to nearest integer 0
+scalb ieee.3m exponent adjustment 0
+sin sin.3m trigonometric function 1
+sinh sinh.3m hyperbolic function 3
+sqrt sqrt.3m square root 1
+tan sin.3m trigonometric function 3
+tanh sinh.3m hyperbolic function 3
+y0 j0.3m bessel function ???
+y1 j0.3m bessel function ???
+yn j0.3m bessel function ???
+.ta
+.fi
+.SH NOTES
+In 4.3 BSD, distributed from the University of California
+in late 1985, most of the foregoing functions come in two
+versions, one for the double\-precision "D" format in the
+DEC VAX\-11 family of computers, another for double\-precision
+arithmetic conforming to the IEEE Standard 754 for Binary
+Floating\-Point Arithmetic. The two versions behave very
+similarly, as should be expected from programs more accurate
+and robust than was the norm when UNIX was born. For
+instance, the programs are accurate to within the numbers
+of \*(ups tabulated above; an \*(up is one \fIU\fRnit in the \fIL\fRast
+\fIP\fRlace. And the programs have been cured of anomalies that
+afflicted the older math library \fIlibm\fR in which incidents like
+the following had been reported:
+.RS
+sqrt(\-1.0) = 0.0 and log(\-1.0) = \-1.7e38.
+.br
+cos(1.0e\-11) > cos(0.0) > 1.0.
+.br
+pow(x,1.0)
+.if n \
+!=
+.if t \
+\(!=
+x when x = 2.0, 3.0, 4.0, ..., 9.0.
+.br
+pow(\-1.0,1.0e10) trapped on Integer Overflow.
+.br
+sqrt(1.0e30) and sqrt(1.0e\-30) were very slow.
+.RE
+However the two versions do differ in ways that have to be
+explained, to which end the following notes are provided.
+.PP
+\fBDEC VAX\-11 D_floating\-point:\fR
+.PP
+This is the format for which the original math library \fIlibm\fR
+was developed, and to which this manual is still principally
+dedicated. It is \fIthe\fR double\-precision format for the PDP\-11
+and the earlier VAX\-11 machines; VAX\-11s after 1983 were
+provided with an optional "G" format closer to the IEEE
+double\-precision format. The earlier DEC MicroVAXs have no
+D format, only G double\-precision. (Why? Why not?)
+.PP
+Properties of D_floating\-point:
+.RS
+Wordsize: 64 bits, 8 bytes. Radix: Binary.
+.br
+Precision: 56
+.if n \
+sig.
+.if t \
+significant
+bits, roughly like 17
+.if n \
+sig.
+.if t \
+significant
+decimals.
+.RS
+If x and x' are consecutive positive D_floating\-point
+numbers (they differ by 1 \*(up), then
+.br
+1.3e\-17 < 0.5**56 < (x'\-x)/x \(<= 0.5**55 < 2.8e\-17.
+.RE
+.nf
+.ta \w'Range:'u+1n +\w'Underflow threshold'u+1n +\w'= 2.0**127'u+1n
+Range: Overflow threshold = 2.0**127 = 1.7e38.
+ Underflow threshold = 0.5**128 = 2.9e\-39.
+ NOTE: THIS RANGE IS COMPARATIVELY NARROW.
+.ta
+.fi
+.RS
+Overflow customarily stops computation.
+.br
+Underflow is customarily flushed quietly to zero.
+.br
+CAUTION:
+.RS
+It is possible to have x
+.if n \
+!=
+.if t \
+\(!=
+y and yet
+x\-y = 0 because of underflow. Similarly
+x > y > 0 cannot prevent either x\(**y = 0
+or y/x = 0 from happening without warning.
+.RE
+.RE
+Zero is represented ambiguously.
+.RS
+Although 2**55 different representations of zero are accepted by
+the hardware, only the obvious representation is ever produced.
+There is no \-0 on a VAX.
+.RE
+.If
+is not part of the VAX architecture.
+.br
+Reserved operands:
+.RS
+of the 2**55 that the hardware
+recognizes, only one of them is ever produced.
+Any floating\-point operation upon a reserved
+operand, even a MOVF or MOVD, customarily stops
+computation, so they are not much used.
+.RE
+Exceptions:
+.RS
+Divisions by zero and operations that
+overflow are invalid operations that customarily
+stop computation or, in earlier machines, produce
+reserved operands that will stop computation.
+.RE
+Rounding:
+.RS
+Every rational operation (+, \-, \(**, /) on a
+VAX (but not necessarily on a PDP\-11), if not an
+over/underflow nor division by zero, is rounded to
+within half an \*(up, and when the rounding error is
+exactly half an \*(up then rounding is away from 0.
+.RE
+.RE
+.PP
+Except for its narrow range, D_floating\-point is one of the
+better computer arithmetics designed in the 1960's.
+Its properties are reflected fairly faithfully in the elementary
+functions for a VAX distributed in 4.3 BSD.
+They over/underflow only if their results have to lie out of range
+or very nearly so, and then they behave much as any rational
+arithmetic operation that over/underflowed would behave.
+Similarly, expressions like log(0) and atanh(1) behave
+like 1/0; and sqrt(\-3) and acos(3) behave like 0/0;
+they all produce reserved operands and/or stop computation!
+The situation is described in more detail in manual pages.
+.RS
+.ll -0.5i
+\fIThis response seems excessively punitive, so it is destined
+to be replaced at some time in the foreseeable future by a
+more flexible but still uniform scheme being developed to
+handle all floating\-point arithmetic exceptions neatly.
+See infnan(3M) for the present state of affairs.\fR
+.ll +0.5i
+.RE
+.PP
+How do the functions in 4.3 BSD's new \fIlibm\fR for UNIX
+compare with their counterparts in DEC's VAX/VMS library?
+Some of the VMS functions are a little faster, some are
+a little more accurate, some are more puritanical about
+exceptions (like pow(0.0,0.0) and atan2(0.0,0.0)),
+and most occupy much more memory than their counterparts in
+\fIlibm\fR.
+The VMS codes interpolate in large table to achieve
+speed and accuracy; the \fIlibm\fR codes use tricky formulas
+compact enough that all of them may some day fit into a ROM.
+.PP
+More important, DEC regards the VMS codes as proprietary
+and guards them zealously against unauthorized use. But the
+\fIlibm\fR codes in 4.3 BSD are intended for the public domain;
+they may be copied freely provided their provenance is always
+acknowledged, and provided users assist the authors in their
+researches by reporting experience with the codes.
+Therefore no user of UNIX on a machine whose arithmetic resembles
+VAX D_floating\-point need use anything worse than the new \fIlibm\fR.
+.PP
+\fBIEEE STANDARD 754 Floating\-Point Arithmetic:\fR
+.PP
+This standard is on its way to becoming more widely adopted
+than any other design for computer arithmetic.
+VLSI chips that conform to some version of that standard have been
+produced by a host of manufacturers, among them ...
+.nf
+.ta 0.5i +\w'Intel i8070, i80287'u+6n
+ Intel i8087, i80287 National Semiconductor 32081
+ Motorola 68881 Weitek WTL-1032, ... , -1165
+ Zilog Z8070 Western Electric (AT&T) WE32106.
+.ta
+.fi
+Other implementations range from software, done thoroughly
+in the Apple Macintosh, through VLSI in the Hewlett\-Packard
+9000 series, to the ELXSI 6400 running ECL at 3 Megaflops.
+Several other companies have adopted the formats
+of IEEE 754 without, alas, adhering to the standard's way
+of handling rounding and exceptions like over/underflow.
+The DEC VAX G_floating\-point format is very similar to the IEEE
+754 Double format, so similar that the C programs for the
+IEEE versions of most of the elementary functions listed
+above could easily be converted to run on a MicroVAX, though
+nobody has volunteered to do that yet.
+.PP
+The codes in 4.3 BSD's \fIlibm\fR for machines that conform to
+IEEE 754 are intended primarily for the National Semi. 32081
+and WTL 1164/65. To use these codes with the Intel or Zilog
+chips, or with the Apple Macintosh or ELXSI 6400, is to
+forego the use of better codes provided (perhaps freely) by
+those companies and designed by some of the authors of the
+codes above.
+Except for \fIatan\fR, \fIcabs\fR, \fIcbrt\fR, \fIerf\fR,
+\fIerfc\fR, \fIhypot\fR, \fIj0\-jn\fR, \fIlgamma\fR, \fIpow\fR
+and \fIy0\-yn\fR,
+the Motorola 68881 has all the functions in \fIlibm\fR on chip,
+and faster and more accurate;
+it, Apple, the i8087, Z8070 and WE32106 all use 64
+.if n \
+sig.
+.if t \
+significant
+bits.
+The main virtue of 4.3 BSD's
+\fIlibm\fR codes is that they are intended for the public domain;
+they may be copied freely provided their provenance is always
+acknowledged, and provided users assist the authors in their
+researches by reporting experience with the codes.
+Therefore no user of UNIX on a machine that conforms to
+IEEE 754 need use anything worse than the new \fIlibm\fR.
+.PP
+Properties of IEEE 754 Double\-Precision:
+.RS
+Wordsize: 64 bits, 8 bytes. Radix: Binary.
+.br
+Precision: 53
+.if n \
+sig.
+.if t \
+significant
+bits, roughly like 16
+.if n \
+sig.
+.if t \
+significant
+decimals.
+.RS
+If x and x' are consecutive positive Double\-Precision
+numbers (they differ by 1 \*(up), then
+.br
+1.1e\-16 < 0.5**53 < (x'\-x)/x \(<= 0.5**52 < 2.3e\-16.
+.RE
+.nf
+.ta \w'Range:'u+1n +\w'Underflow threshold'u+1n +\w'= 2.0**1024'u+1n
+Range: Overflow threshold = 2.0**1024 = 1.8e308
+ Underflow threshold = 0.5**1022 = 2.2e\-308
+.ta
+.fi
+.RS
+Overflow goes by default to a signed
+.If "" .
+.br
+Underflow is \fIGradual,\fR rounding to the nearest
+integer multiple of 0.5**1074 = 4.9e\-324.
+.RE
+Zero is represented ambiguously as +0 or \-0.
+.RS
+Its sign transforms correctly through multiplication or
+division, and is preserved by addition of zeros
+with like signs; but x\-x yields +0 for every
+finite x. The only operations that reveal zero's
+sign are division by zero and copysign(x,\(+-0).
+In particular, comparison (x > y, x \(>= y, etc.)
+cannot be affected by the sign of zero; but if
+finite x = y then
+.If
+\&= 1/(x\-y)
+.if n \
+!=
+.if t \
+\(!=
+\-1/(y\-x) =
+.If \- .
+.RE
+.If
+is signed.
+.RS
+it persists when added to itself
+or to any finite number. Its sign transforms
+correctly through multiplication and division, and
+.If (finite)/\(+- \0=\0\(+-0
+(nonzero)/0 =
+.If \(+- .
+But
+.if n \
+Infinity\-Infinity, Infinity\(**0 and Infinity/Infinity
+.if t \
+\(if\-\(if, \(if\(**0 and \(if/\(if
+are, like 0/0 and sqrt(\-3),
+invalid operations that produce \*(nn. ...
+.RE
+Reserved operands:
+.RS
+there are 2**53\-2 of them, all
+called \*(nn (\fIN\fRot \fIa N\fRumber).
+Some, called Signaling \*(nns, trap any floating\-point operation
+performed upon them; they are used to mark missing
+or uninitialized values, or nonexistent elements
+of arrays. The rest are Quiet \*(nns; they are
+the default results of Invalid Operations, and
+propagate through subsequent arithmetic operations.
+If x
+.if n \
+!=
+.if t \
+\(!=
+x then x is \*(nn; every other predicate
+(x > y, x = y, x < y, ...) is FALSE if \*(nn is involved.
+.br
+NOTE: Trichotomy is violated by \*(nn.
+.RS
+Besides being FALSE, predicates that entail ordered
+comparison, rather than mere (in)equality,
+signal Invalid Operation when \*(nn is involved.
+.RE
+.RE
+Rounding:
+.RS
+Every algebraic operation (+, \-, \(**, /,
+.if n \
+sqrt)
+.if t \
+\(sr)
+is rounded by default to within half an \*(up, and
+when the rounding error is exactly half an \*(up then
+the rounded value's least significant bit is zero.
+This kind of rounding is usually the best kind,
+sometimes provably so; for instance, for every
+x = 1.0, 2.0, 3.0, 4.0, ..., 2.0**52, we find
+(x/3.0)\(**3.0 == x and (x/10.0)\(**10.0 == x and ...
+despite that both the quotients and the products
+have been rounded. Only rounding like IEEE 754
+can do that. But no single kind of rounding can be
+proved best for every circumstance, so IEEE 754
+provides rounding towards zero or towards
+.If +
+or towards
+.If \-
+at the programmer's option. And the
+same kinds of rounding are specified for
+Binary\-Decimal Conversions, at least for magnitudes
+between roughly 1.0e\-10 and 1.0e37.
+.RE
+Exceptions:
+.RS
+IEEE 754 recognizes five kinds of floating\-point exceptions,
+listed below in declining order of probable importance.
+.RS
+.nf
+.ta \w'Invalid Operation'u+6n +\w'Gradual Underflow'u+2n
+Exception Default Result
+.tc \(ru
+
+.tc
+Invalid Operation \*(nn, or FALSE
+.if n \{\
+Overflow \(+-Infinity
+Divide by Zero \(+-Infinity \}
+.if t \{\
+Overflow \(+-\(if
+Divide by Zero \(+-\(if \}
+Underflow Gradual Underflow
+Inexact Rounded value
+.ta