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Name

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

Synopsis

cc [ flag ... ] file ... -lm [ library ... ]

#include <math.h>

double frexp(double value, int *eptr);

double ldexp(double value, int exp);

double logb(double value);

double modf(double value, double *iptr);

float modff(float value, float *iptr);

double nextafter(double value1, double value2);

double scalb(double value, double exp);

MT-Level

MT-Safe

Description

Every non-zero number can be written uniquely as x* 2un d, 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* 2uexp d. 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.

Return Values

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 +2u-1022 d and

-2u-1022 d. In both cases errno is set to ERANGE .

Table of Contents