ultrix man page for finite

ieee(3m)																  ieee(3m)

Name
       copysign, drem, finite, logb, scalb - copysign, remainder, exponent manipulations

Syntax
       #include <math.h>

       double copysign(x,y)
       double x,y;

       double drem(x,y)
       double x,y;

       int finite(x)
       double x;

       double logb(x)
       double x;

       double scalb(x,n)
       double x;
       int n;

Description
       These functions are required, or recommended by the IEEE standard 754 for floating-point arithmetic.

       The function returns x with its sign changed to y's.

       The function returns the remainder r := x - n*y where n is the integer nearest the exact value of x/y.  Additionally if |n-x/y|=1/2, then n
       is even.  Consequently the remainder is computed exactly and |r| <= |y|/2.  Note that is the exception (see Diagnostics).

       Finite(x) = 1 just when -infinity < x < +infinity,
		 = 0 otherwise (when |x| = infinity or x is NaN)

       The a signed integer converted to double-precision floating-point and so chosen that 1 <= |x|/2**n < 2 unless x = 0 or |x| = infinity or  x
       lies between 0 and the Underflow Threshold.

       Scalb(x,n) = x*(2**n) computed, for integer n, without first computing 2**N.

Diagnostics
       IEEE 754 defines drem(x,0) and drem(infinity,y) to be invalid operations that produce a NaN.

       IEEE 754 defines logb(+-infinity) = +infinity and logb(0) = -infinity, requires the latter to signal Division-by-Zero.

Restrictions
       IEEE 754 currently specifies that logb(denormalized no.) = logb(tiniest normalized no. > 0) but the consensus has changed to the specifica-
       tion in the new proposed IEEE standard p854, namely that logb(x) satisfy
	      1 <= scalb(|x|,-logb(x)) < Radix	 ... = 2 for IEEE 754
       for every x except 0, infinity and NaN.	Almost every program that assumes 754's specification will work correctly if  logb  follows  854's
       specification instead.

       IEEE 754 requires copysign(x,NaN) = +-x	but says nothing else about the sign of a NaN.

See Also
       floor(3M), fp_class(3), math(3M)

								       RISC								  ieee(3m)