# Crate fastdivide [−] [src]

# Yes, but what is it really ?

Division is a very costly operation for your CPU. You may have noticed that when the divisor is known at compile time, your compiler transforms the operations into a cryptic combination of a multiplication and bitshift.

Fastdivide is about doing the same trick your compiler uses but when the divisor is unknown at compile time. Of course, it requires preprocessing a datastructure that is specific to your divisor, and using it only makes sense if this preprocessing is amortized by a high number of division (with the same divisor).

# When is it useful ?

If you do a lot (> 10) of division with the same divisor ; and this division is a bottleneck in your program. This is for instance useful to compute histograms.

# Example

use fastdivide::DividerU64; fn histogram(vals: &[u64], min: u64, interval: u64, output: &mut [usize]) { // Preprocessing a datastructure dedicated // to dividing `u64` by `interval`. // // This preprocessing is not cheap. let divide = DividerU64::divide_by(interval); // We reuse the same `Divider` for all of the // values in vals. for &val in vals { if val < min { continue; } let bucket_id = divide.divide(val - min) as usize; if bucket_id < output.len() { output[bucket_id as usize] += 1; } } }

## Structs

DividerU64 |