Re: Fast division (was Re: Suggested method for returning a string from a C program?)

On 26.03.2025 12:40, David Brown wrote:

>
[ substituting a division by multiplication (and some primitives) ]

 
Roughly speaking, when you want division of "y" by a fixed - i.e.,
constant value known at compile time - number "x", you can do it by
pre-calculating z = 2^n / x and then you implement "y / x" by "y * z /
2^n".  (There's also some stuff to handle correct rounding, especially
with signed types.)

Thanks for the terse explanation; the formulas helped me to detect
that the constants in Waldek's assembler code are the pre-computed
reciprocals.

First I thought that there's a trick to avoid division of non-const
expressions.

Janis

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