On 26.03.2025 12:40, David Brown wrote:For non-constant divisors, it's a bit more difficult! If you are going to use the same divisor several times, it can be worth computing the scaled reciprocal, so that you only have one hard operation. I believe that hardware floating point units do that anyway for division.Thanks for the terse explanation; the formulas helped me to detect>>
[ 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.)
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.
| Date | Sujet | # | Auteur | |
| 22 Apr 26 |  … |
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