# logb(3m) [ultrix man page]

ieee(3m) ieee(3m)Namecopysign, drem, finite, logb, scalb - copysign, remainder, exponent manipulationsSyntax#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;DescriptionThese 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< 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.-infinityDiagnosticsIEEE 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) =, requires the latter to signal Division-by-Zero.-infinityRestrictionsIEEE 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 Alsofloor(3M), fp_class(3), math(3M) RISC ieee(3m)

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Namecopysign, drem, finite, logb, scalb - copysign, remainder, exponent manipulationsSyntax#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;DescriptionThese 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< 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.-infinityDiagnosticsIEEE 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) =, requires the latter to signal Division-by-Zero.-infinityRestrictionsIEEE 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 Alsofloor(3M), fp_class(3), math(3M) RISC ieee(3m)