9fans archive / 1997 / 01 / 41 /    prev next

From: rob@pla... rob@pla...
Subject: Primes
Date: Fri, 31 Jan 1997 11:20:24 -0500

The primes mystery was solved, by another venerable person,
without looking at the source.  The primes program uses
floating point and its upper limit is set by the number of
bits in the mantissa.  When moved from PDP-11 floating point
to IEEE, two bits of mantissa were lost but the source
wasn't fixed to represent the loss.  To repair the program,
change the variable 'big' from 2^(64-8) to 2^(64-10), if
I remember the format of IEEE numbers correctly.

-rob