floor.3m

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 3M 代码 · 共 128 行

.TH floor 3m RISC
.SH Name
floor, ffloor, fabs, ceil, ceil, trunc, ftrunc, fmod, rint \- floor, absolute value, ceiling, truncation, floating point remainder and round-to-nearest functions
.SH Syntax
.nf
.B #include <math.h>
.PP
.B double floor(\fIx\fP)
.B double \fIx\fP;
.PP
.B float ffloor(\fIx\fP)
.B float \fIx\fP;
.PP
.B double ceil(\fIx\fP)
.B double \fIx\fP;
.PP
.B float fceil(\fIx\fP)
.B float \fIx\fP;
.PP
.B double trunc(\fIx\fP)
.B double \fIx\fP;
.PP
.B float ftrunc(\fIx\fP)
.B float \fIx\fP;
.PP
.B double fabs(\fIx\fP)
.B double \fIx\fP;
.PP
.B double fmod (\fIx, y\fP)
.B double \fIx, y\fP;
.PP
.B double rint(\fIx\fP)
.B double \fIx\fP;
.fi
.SH Description
.NXR "fabs subroutine"
.NXR "ceil subroutine"
.NXR "floor function" "returning integer"
.NXR "ceiling function" "returning integer"
.NXR "truncation"
.NXR "absolute value function"
.NXR "floating point remainder"
.NXR "round-to-nearest function"
The 
.PN floor
and 
.PN ffloor
routines return the largest integer which is not greater than x
for double and float data types, respectively.
.PP
The 
.PN ceil
and
.PN fceil
routines return the smallest integer which is not less than x
for double and float data types, respectively.
.PP
The
.PN trunc
and
.PN ftrunc
routines return the integer (represented as a floating-point number)
of x with the fractional bits truncated
for double and float data types respectively.
.PP
The 
.PN fabs
routine returns the absolute value |\|x|.
.PP
The
.PN fmod
routine returns the floating point remainder of the division of
.I x\^
by
.IR y :
zero if
.I y\^
is zero or if
.I x/y\^
would overflow;
otherwise the number
.I f\^
with the same sign as
.IR x ,
such that
.I "x = iy + f"
for some integer
.IR i ,
and
.RI | \|f "| < |" \|y |\|.
.PP
The
.PN rint
routine returns the integer (represented as a double precision number)
nearest x in the direction of the prevailing rounding mode.
.PP
In the default rounding mode, to nearest,
.PN rint(x) 
is the integer nearest x with the additional stipulation
that if |rint(x)\-x|=1/2 then 
.PN rint(x) 
is even.
Other rounding modes can make 
.PN rint 
act like 
.PN floor
or
.PN ceil ,
or round towards zero.
.PP
Another way to obtain an integer near x is to declare (in C)
.RS
double x;\0\0\0\0 int k;\0\0\0\0k\0=\0x;
.RE
The C compiler rounds x towards 0 to get the integer k.
Also note that, if x is larger than k can accommodate, the value of
k and the presence or absence of an integer overflow are hard to
predict.
.PP
The 
.PN fabs 
routine 
is in libc.a rather than libm.a.
.SH See Also
abs(3),
ieee(3m),
math(3m)