Looking for extended precision integer arith pkg

[Marcus Leech]

I'm looking for an extended-precision arithmetic package for C
 that has the following attributes:

at least 48-bits and up to 64-bits

must have:

compare
ascii-representation<-->extended integer
int<-->extended integer
add, sub, mul, div

There used to be an "mp" package, but not all vendors support this, so I'd
  like a public-domain/shareware package.

Please reply by mail.

--
Marcus Leech, 4Y11             Bell-Northern Research  |opinions expressed
mleech at bnr.ca                  P.O. Box 3511, Stn. C   |are my own, and not
VE3MDL at VE3JF.ON.CAN.NA         Ottawa, ON, CAN K1Y 4H7 |necessarily BNRs