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trapov(3f) [bsd man page]

TRAPOV(3F)																TRAPOV(3F)

NAME
trapov - trap and repair floating point overflow SYNOPSIS
subroutine trapov (numesg, rtnval) double precision rtnval DESCRIPTION
NOTE: This routine applies only to the older VAX 11/780's. VAX computers made or upgraded since spring 1983 handle errors differently. See trpfpe(3F) for the newer error handler. This routine has always been ineffective on the VAX 11/750. It is a null routine on the PDP11. This call sets up signal handlers to trap arithmetic exceptions and the use of illegal operands. Trapping arithmetic exceptions allows the user's program to proceed from instances of floating point overflow or divide by zero. The result of such operations will be an illegal floating point value. The subsequent use of the illegal operand will be trapped and the operand replaced by the specified value. The first numesg occurrences of a floating point arithmetic error will cause a message to be written to the standard error file. If the resulting value is used, the value given for rtnval will replace the illegal operand generated by the arithmetic error. Rtnval must be a double precision value. For example, ``0d0'' or ``dflmax()''. FILES
/usr/lib/libF77.a SEE ALSO
trpfpe(3F), signal(3F), range(3F) BUGS
Other arithmetic exceptions can be trapped but not repaired. There is no way to distinguish between an integer value of 32768 and the illegal floating point form. Therefore such an integer value may get replaced while repairing the use of an illegal operand. 4.2 Berkeley Distribution May 15, 1985 TRAPOV(3F)

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IEEE(3M)																  IEEE(3M)

NAME
copysign, drem, finite, logb, scalb - copysign, remainder, exponent manipulations SYNOPSIS
#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 for, or recommended by the IEEE standard 754 for floating-point arithmetic. Copysign(x,y) returns x with its sign changed to y's. Drem(x,y) 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. Finite(x) = 1 just when -infinity < x < +infinity, = 0 otherwise (when |x| = infinity or x is NaN or x is the VAX's reserved operand.) Logb(x) 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| = infinity or x lies between 0 and the Underflow Threshold; see below under "BUGS". 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. On a VAX, drem(x,0) returns the reserved op- erand. No infinity exists on a VAX. IEEE 754 defines logb(+-infinity) = +infinity and logb(0) = -infinity, 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(x,n) would overflow on a VAX, it returns the reserved oper- and and sets errno to ERANGE. SEE ALSO
floor(3M), math(3M), infnan(3M) AUTHOR
Kwok-Choi Ng BUGS
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 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. 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 May 12, 1986 IEEE(3M)

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