Re: [HACKERS] Re: Trouble with float4 after upgrading from 6.5.3 to 7.0.2

Philip Warner <pjw(at)rhyme(dot)com(dot)au> writes:
> pjw=# select float8(float4(10.1));
> float8
> ------------------
> 10.1000003814697
> (1 row)

> I would have expected the latter to be at worst 10.10000000000000 +/-
> .00000000000001.

float4 is good to about 7 decimal digits (24 mantissa bits) on
IEEE-standard machines. Thus the above result is actually closer
than you have any right to expect.

Don't they teach people about float arithmetic in CS 101 anymore?

regards, tom lane