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The functions described in this section are primarily provided as a way to efficiently perform certain low-level manipulations on floating point numbers that are represented internally using a binary radix; see Floating Point Concepts. These functions are required to have equivalent behavior even if the representation does not use a radix of 2, but of course they are unlikely to be particularly efficient in those cases.
All these functions are declared in math.h.
These functions are used to split the number value into a normalized fraction and an exponent.
If the argument value is not zero, the return value is value
times a power of two, and its magnitude is always in the range 1/2
(inclusive) to 1 (exclusive). The corresponding exponent is stored in
*exponent
; the return value multiplied by 2 raised to this
exponent equals the original number value.
For example, frexp (12.8, &exponent)
returns 0.8
and
stores 4
in exponent
.
If value is zero, then the return value is zero and
zero is stored in *exponent
.
These functions return the result of multiplying the floating-point
number value by 2 raised to the power exponent. (It can
be used to reassemble floating-point numbers that were taken apart
by frexp
.)
For example, ldexp (0.8, 4)
returns 12.8
.
The following functions, which come from BSD, provide facilities
equivalent to those of ldexp
and frexp
. See also the
ISO C function logb
which originally also appeared in BSD.
The scalb
function is the BSD name for ldexp
.
scalbn
is identical to scalb
, except that the exponent
n is an int
instead of a floating-point number.
scalbln
is identical to scalb
, except that the exponent
n is a long int
instead of a floating-point number.
significand
returns the mantissa of x scaled to the range
[1, 2).
It is equivalent to scalb (x, (double) -ilogb (x))
.
This function exists mainly for use in certain standardized tests of IEEE 754 conformance.
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