ieee man page on 4.4BSD

Man page or keyword search:  
man Server   1065 pages
apropos Keyword Search (all sections)
Output format
4.4BSD logo
[printable version]

IEEE(3)			 BSD Library Functions Manual		       IEEE(3)

     copysign, drem, finite, logb, scalb — IEEE 754 floating point support

     #include <math.h>

     copysign(double x, double y);

     drem(double x, double y);

     finite(double x);

     logb(double x);

     scalb(double x, int n);

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

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

     The drem() function returns the remainder r := x - n∗y where n is the
     integer nearest the exact value of x/y; moreover if |n - x/y| = 1/2 then
     n is even.	 Consequently the remainder is computed exactly and |r| ≤
     |y|/2. But drem(x, 0) is exceptional.  (See below under DIAGNOSTICS.)

     The finite() function returns the value 1 just when -∞ < x < +∞; other‐
     wise a zero is returned (when |x| = ∞ or x is NaN or is the VAX's
     reserved operand).

     The logb() function returns x's exponent n, a signed integer converted to
     double-precision floating-point and so chosen that 1 (<= |x|2**n < 2
     unless x = 0 or (only on machines that conform to IEEE 754) |x| = ∞ or x
     lies between 0 and the Underflow Threshold.  (See below under BUGS.)

     The scalb() function returns x∗(2**n) computed, for integer n, without
     first computing 2∗n.

     The IEEE standard 754 defines drem(x, 0) and drem(∞, y) to be invalid
     operations that produce a NaN.  On the VAX, drem(x, 0) generates a
     reserved operand fault.  No ∞ exists on a VAX.

     IEEE 754 defines logb(±∞) = ∞ and logb(0) = -∞, and requires the latter
     to signal Division-by-Zero.  But on a VAX, logb(0) = 1.0 - 2.0**31 =
     -2,147,483,647.0.	And if the correct value of scalb() would overflow on
     a VAX, it generates a reserved operand fault and sets the global variable
     errno to ERANGE.

     floor(3), math(3), infnan(3)

     The ieee functions appeared in 4.3BSD.

     Should drem(x, 0) and logb(0) on a VAX signal invalidity by setting errno
     = EDOM?  Should logb(0) return  -1.7e38?

     IEEE 754 currently specifies that logb(denormalized no.)  = logb(tiniest
     normalized no. > 0) but the consensus has changed to the specification 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, ∞ and NaN.  Almost every program that assumes 754's
     specification will work correctly if logb() follows 854's specification

     IEEE 754 requires copysign(x, NaN)) = ±x but says nothing else about the
     sign of a NaN.  A NaN (Not a Number) is similar in spirit to the VAX's
     reserved operand, but very different in important details.	 Since the
     sign bit of a reserved operand makes it look negative,

	   copysign(x, reserved operand) = -x;

     should this return the reserved operand instead?

4.3 Berkeley Distribution	 June 4, 1993	     4.3 Berkeley Distribution

List of man pages available for 4.4BSD

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net