Description

   The gcvt function places the converted string in a buffer and
   returns the address of the buffer. If possible, gcvt produces
   ndigit significant digits in F-format, or if not possible, in
   E-format. Trailing zeros are suppressed.

   The ecvt, fcvt, and gcvt functions represent the following
   special values specified in the IEEE Standard for floating-point
   arithmetic:

   Value         Representation

   Quiet NaN     NaNQ
   Signalling    NaNS
   NaN
   +Infinity     Infinity
   -Infinity     -Infinity

   The sign associated with each of these values is stored into the
   sign argument. In IEEE floating-point representation, a value
   of 0 (zero) can be positive or negative, as set by the sign
   argument.

   See also fcvt and ecvt.