exponent

Function: exponent
Section: conversions
C-Name: gpexponent
Prototype: G
Help: exponent(x): binary exponent of x
Doc: When $x$ is a \typ{REAL}, the result is the binary exponent $e$ of $x$.
 For a nonzero $x$, this is the unique integer $e$ such that
 $2^e \leq |x| < 2^{e+1}$. For a real $0$, this returns the PARI exponent $e$
 attached to $x$ (which may represent any floating-point number less than
 $2^e$ in absolute value).
 \bprog
 ? exponent(Pi)
 %1 = 1
 ? exponent(4.0)
 %2 = 2
 ? exponent(0.0)
 %3 = -128
 ? default(realbitprecision)
 %4 = 128
 @eprog\noindent This definition extends naturally to nonzero integers,
 and the exponent of an exact $0$ is $-\kbd{oo}$ by convention.

 For convenience, we \emph{define} the exponent of a \typ{FRAC} $a/b$ as
 the difference of \kbd{exponent}$(a)$ and \kbd{exponent}$(b)$; note that,
 if $e'$ denotes the exponent of \kbd{$a/b$ * 1.0}, then the exponent $e$
 we return is either $e'$ or $e'+1$, thus $2^{e+1}$ is an upper bound for
 $|a/b|$.
 \bprog
 ? [ exponent(9), exponent(10), exponent(9/10), exponent(9/10*1.) ]
 %5 = [3, 3, 0, -1]
 @eprog

 For a PARI object of type \typ{COMPLEX}, \typ{POL}, \typ{SER}, \typ{VEC},
 \typ{COL}, \typ{MAT} this returns the largest exponent found among the
 components of $x$. Hence $2^{e+1}$ is a quick upper bound for the sup norm
 of real matrices or polynomials; and $2^{e+(3/2)}$ for complex ones.

 \bprog
 ? exponent(3*x^2 + 15*x - 100)
 %5 = 6
 ? exponent(0)
 %6 = -oo
 @eprog