[edit]Parameters

[edit]Return value

Ifarg is zero, returns zero and stores zero in*exp.

Otherwise (ifarg is not zero), if no errors occur, returns the valuex in the range(-1;-0.5], [0.5; 1) and stores an integer value in*exp such thatx×2(*exp)
=arg.

If the value to be stored in*exp is outside the range ofint, the behavior is unspecified.

Ifarg is not a floating-point number, the behavior is unspecified.

[edit]Error handling

This function is not subject to any errors specified inmath_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

• Ifarg is ±0, it is returned, unmodified, and0 is stored in*exp.
• Ifarg is ±∞, it is returned, and an unspecified value is stored in*exp.
• Ifarg is NaN, NaN is returned, and an unspecified value is stored in*exp.
• No floating-point exceptions are raised.
• IfFLT_RADIX is2 (or a power of 2), the returned value is exact,the current rounding mode is ignored.

[edit]Notes

On a binary system (whereFLT_RADIX is2),frexp may be implemented as

{*exp=(value==0)?0:(int)(1+logb(value));returnscalbn(value,-(*exp));}

The functionfrexp, together with its dual,ldexp, can be used to manipulate the representation of a floating-point number without direct bit manipulations.

[edit]Example

#include <float.h>#include <math.h>#include <stdio.h> int main(void){double f=123.45;printf("Given the number %.2f or %a in hex,\n", f, f); double f3;double f2=modf(f,&f3);printf("modf() makes %.0f + %.2f\n", f3, f2); int i;    f2= frexp(f,&i);printf("frexp() makes %f * 2^%d\n", f2, i);     i=ilogb(f);printf("logb()/ilogb() make %f * %d^%d\n", f/scalbn(1.0, i),FLT_RADIX, i);}

Given the number 123.45 or 0x1.edccccccccccdp+6 in hex,modf() makes 123 + 0.45frexp() makes 0.964453 * 2^7logb()/ilogb() make 1.92891 * 2^6

[edit]References

[edit]See also

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