Promotion rules ... why no float?

[deadalnix via Digitalmars-d]

On Wednesday, 7 September 2016 at 14:46:46 UTC, Sai wrote:
> I suspected the same, most of the CPUs support fast floating 
> point operations anyway (with FPUs), shouldn't take a lot more 
> time than doing integer arithmetic. Unless we are targeting 
> 8bit avr or something similar.
>

No. Floating point in binaries are represented as
v = m * 2 ^ e

Now:

v0 / v1 = (m0 * 2 ^ e0) / (m1 * 2 ^ e1)
v0 / v1 = (m0 / m1) * 2 ^ (e0 - e1)

ie to do a 32 bits float division, you need to do a 24 bits 
integer division, while when doing a 32bits integer division you 
need to do a 32bits integer division (!)

The same apply to floating point multiply that are usually faster 
than integer multiply. In fact, on some machines, multiplying 
floats is faster than adding them.