# ftoi(3) [ultrix man page]

ftoi(3) Library Functions Manual ftoi(3)Nameftoi, itof, dtoi, itod, gtoi, itog - convert floating values between VAX and IEEE formatSyntaxint ftoi(value) float *value; int itof(value) float *value; int dtoi(value) double *value; int itod(value) double *value; int gtoi(value) double *value; int itog(value) double *value;DescriptionThe following C library functions convert floating values between VAX and IEEE formats. The function converts the specified VAX ffloat number to IEEE single-precision format. It returns zero if successful and nonzero without performing the conversion if not successful (for example, underflow). The function converts the specified IEEE single-precision number to VAX ffloat format. It returns zero if successful and nonzero without performing the conversion if not successful (for example, overflow). The function converts the specified VAX dfloat number to IEEE double-precision format. It returns zero if successful and nonzero without performing the conversion if not successful (for example, underflow). The function converts the specified IEEE double-precision number to VAX dfloat format. It returns zero if successful and nonzero without performing the conversion if not successful (for example, underflow or overflow). The function converts the specified VAX gfloat number to IEEE double-precision format. It returns zero if successful and nonzero without performing the conversion if not successful (for example, underflow). The function converts the specified IEEE double-precision number to VAX gfloat format. It returns zero if successful and nonzero without performing the conversion if not successful (for example, underflow). ftoi(3)

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IEEE(3M) IEEE(3M)NAME

copysign, drem, finite, logb, scalb - copysign, remainder, exponent manipulationsSYNOPSIS

#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< 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.-infinityDIAGNOSTICS

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) =, requires the latter to signal Division-by-Zero. But on a VAX, logb(0) = 1.0 - 2.0**31 =-infinity,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.-2SEE ALSO

floor(3M), math(3M), infnan(3M)AUTHOR

Kwok-Choi NgBUGS

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 DistributionMay 12, 1986 IEEE(3M)