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

At 12:11 7/08/00 -0400, Tom Lane wrote:
>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?
>

No idea. It's a couple of decades since I did it.

I wasn't complaining about the float4 accuracy; I was complaining about the
way it was converted to float8. It seems more intuitive to zero-extend base
10 zeros...

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