NAME

frexp, ldexp, logb, modf, modff, nextafter, scalb − manipulate parts of floating-point numbers

SYNOPSIS

#include <math.h>

double frexp (double value, int ∗eptr);

double ldexp (double value, int exp);

double logb (double value);

double nextafter (double value1, double value2);

double scalb (double value, double exp);

double modf (double value, double ∗iptr);

float modff (float value, float ∗iptr);

DESCRIPTION

Every non-zero number can be written uniquely as x∗ 2n, where the “mantissa” (fraction) x is in the range 0.5 ≤ |x| < 1.0, and the “exponent” n is an integer.  frexp returns the mantissa of a double value, and stores the exponent indirectly in the location pointed to by eptr. If value is zero, both results returned by frexp are zero. 

ldexp and scalb return the quantity value∗ 2exp. The only difference between the two is that scalb of a signaling NaN will result in the invalid operation exception being raised. 

logb returns the unbiased exponent of its floating-point argument as a double-precision floating-point value. 

modf and modff (single-precision version) return the signed fractional part of value and store the integral part indirectly in the location pointed to by iptr.

nextafter returns the next representable double-precision floating-point value following value1 in the direction of value2.  Thus, if value2 is less than value1, ­nextafter returns the largest representable floating-point number less than value1. 

SEE ALSO

cc(1), intro(3M)

DIAGNOSTICS

If ldexp would cause overflow, ±HUGE (defined in math.h) is returned (according to the sign of value), and errno is set to ERANGE.  If ldexp would cause underflow, zero is returned and errno is set to ERANGE.  If the input value to ldexp is NaN or infinity, that input is returned and errno is set to EDOM.  The same error conditions apply to scalb except that a signaling NaN as input will result in the raising of the invalid operation exception. 

logb of NaN returns that NaN, logb of infinity returns positive infinity, and logb of zero returns negative infinity and results in the raising of the divide by zero exception.  In each of these conditions errno is set to EDOM. 

If input value1 to nextafter is positive or negative infinity, that input is returned and errno is set to EDOM.  The overflow and inexact exceptions are signalled when input value1 is finite, but nextafter(value1, value2) is not.  The underflow and inexact exceptions are signalled when nextafter(value1, value2) lies strictly between ±2−1022.  In both cases errno is set to ERANGE. 

When the program is compiled with the cc options −Xc or −Xa, HUGE_VAL is returned instead of HUGE.

  —  C Development Set