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Ratio64: implement nearest fraction algorithm

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This commit is contained in:
Quaternions 2023-10-13 19:08:22 -07:00
parent 80b1d25a13
commit d33b830338
1 changed files with 26 additions and 4 deletions
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30
src/integer.rs
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@ -148,17 +148,39 @@ pub enum Ratio64TryFromFloatError{
HighlyNegativeExponent(i16),
HighlyPositiveExponent(i16),
}
const MAX_DENOMINATOR:u128=u64::MAX as u128;
#[inline]
fn ratio64_from_mes((m,e,s):(u64,i16,i8))->Result<Ratio64,Ratio64TryFromFloatError>{
if e< -127{
//bye bye
//this can also just be zero
Err(Ratio64TryFromFloatError::HighlyNegativeExponent(e))
}else if e< -63{
//TODO
Err(Ratio64TryFromFloatError::HighlyNegativeExponent(e))
//approximate input ratio within denominator limit
let mut target_num=m as u128;
let mut target_den=1u128<<-e;
let mut num=1;
let mut den=0;
let mut prev_num=0;
let mut prev_den=1;
while target_den!=0{
let whole=target_num/target_den;
(target_num,target_den)=(target_den,target_num-whole*target_den);
let new_num=whole*num+prev_num;
let new_den=whole*den+prev_den;
if MAX_DENOMINATOR<new_den{
break;
}else{
(prev_num,prev_den)=(num,den);
(num,den)=(new_num,new_den);
}
}
Ok(Ratio64::new(num as i64,den as u64).unwrap())
}else if e<0{
Ok(Ratio64::new((m as i64)*(s as i64),1<<-e).unwrap())
}else if e<62-52{
}else if (64-m.leading_zeros() as i16)+e<64{
Ok(Ratio64::new((m as i64)*(s as i64)*(1<<e),1).unwrap())
}else{
Err(Ratio64TryFromFloatError::HighlyPositiveExponent(e))