Function: sinc
Section: transcendental
C-Name: gsinc
Prototype: Gp
Description:
 (mp):real:prec      gsinc($1, $prec)
 (gen):gen:prec      gsinc($1, $prec)
Help: sinc(x): sinc function of x.
Doc: cardinal sine of $x$, i.e. $\sin(x)/x$ if $x\neq 0$, $1$ otherwise.
 Note that this function also allows to compute
 $$(1-\cos(x)) / x^{2} = \kbd{sinc}(x/2)^{2} / 2$$
 accurately near $x = 0$.
