Add precomputed constants for common cases.

There are now 2 features that control the amount of precomputed
constants. They can either be 0, 12, or 256. Most users will likely want
to go with the 12, so this is the default feature.

1 files changed, 10 insertions, 3 deletions

diff --git a/src/passwordmaker/base_conversion/iterative_conversion_impl/mod.rs b/src/passwordmaker/base_conversion/iterative_conversion_impl/mod.rs
index ae4aeca..5397f03 100644
--- a/src/passwordmaker/base_conversion/iterative_conversion_impl/mod.rs
+++ b/src/passwordmaker/base_conversion/iterative_conversion_impl/mod.rs
@@ -4,8 +4,10 @@
 
 //let's start with the simple case: u128
 //we do need a NewType here, because actual u128 already has a Mul<&usize> implementation that does not match the version we want.
-
+#[cfg(feature="precomputed_max_powers")]
 mod precomputed_constants;
+#[cfg(all(not(feature="precomputed_max_powers"),feature="precomputed_common_max_powers"))]
+mod precomputed_common_constants;
 
 use std::ops::{DivAssign, Mul};
 use std::convert::{TryFrom, TryInto};
@@ -13,7 +15,7 @@ use std::fmt::Display;
 use std::error::Error;
 use std::iter::once;
 
-use super::iterative_conversion::{RemAssignWithQuotient, ConstantMaxPowerCache};
+use super::iterative_conversion::{RemAssignWithQuotient, PrecomputedMaxPowers};
 
 //Type to be used as V, with usize as B.
 pub(crate) struct SixteenBytes(u128);
@@ -68,7 +70,7 @@ impl Mul<&SixteenBytes> for &SixteenBytes{
     }
 }
 
-impl ConstantMaxPowerCache<usize> for SixteenBytes{}
+impl PrecomputedMaxPowers<usize> for SixteenBytes{}
 
 //--------------------------------------------------------------------------------------------------------------------------------------
 //and now the hard part: The same for [u32;N].
@@ -77,6 +79,11 @@ impl ConstantMaxPowerCache<usize> for SixteenBytes{}
 #[derive(PartialEq, PartialOrd, Ord, Eq, Clone, Debug)]
 pub(crate) struct ArbitraryBytes<const N : usize>([u32;N]);
 
+#[cfg(not(any(feature="precomputed_max_powers", feature="precomputed_common_max_powers")))]
+impl PrecomputedMaxPowers<usize> for ArbitraryBytes<5>{}
+#[cfg(not(any(feature="precomputed_max_powers", feature="precomputed_common_max_powers")))]
+impl PrecomputedMaxPowers<usize> for ArbitraryBytes<8>{}
+
 const fn from_usize<const N : usize>(x : &usize) -> ArbitraryBytes<N> {
     let mut result = [0;N]; //from Godbolt it looks like the compiler is smart enough to skip the unnecessary inits.
     #[cfg(target_pointer_width = "64")]