Rollup merge of #146284 - Kivooeo:blazing-fast-division-bignum, r=Mark-Simulacrum

Remove `div_rem` from `core::num::bignum`
This fixes very old fixme that sounds like this
```
Stupid slow base-2 long division taken from
https://en.wikipedia.org/wiki/Division_algorithm
FIXME use a greater base ($ty) for the long division.
```
By deleting this method since it was never used

Author: matthiaskrgr

library/core/src/num/bignum.rs

@@ -335,43 +335,6 @@ macro_rules! define_bignum {
 }
 (self, borrow)
 }
-
-/// Divide self by another bignum, overwriting `q` with the quotient and `r` with the
-/// remainder.
-pubfn div_rem(&self, d:&$name, q:&mut $name, r:&mut $name){
-// Stupid slow base-2 long division taken from
-// https://en.wikipedia.org/wiki/Division_algorithm
-// FIXME use a greater base ($ty) for the long division.
- assert!(!d.is_zero());
-let digitbits = <$ty>::BITSasusize;
-for digit in &mut q.base[..]{
-*digit = 0;
-}
-for digit in &mut r.base[..]{
-*digit = 0;
-}
- r.size = d.size;
- q.size = 1;
-letmut q_is_zero = true;
-let end = self.bit_length();
-for i in (0..end).rev(){
- r.mul_pow2(1);
- r.base[0] |= self.get_bit(i)as $ty;
-if&*r >= d {
- r.sub(d);
-// Set bit `i` of q to 1.
-let digit_idx = i / digitbits;
-let bit_idx = i % digitbits;
-if q_is_zero {
- q.size = digit_idx + 1;
- q_is_zero = false;
-}
- q.base[digit_idx] |= 1 << bit_idx;
-}
-}
- debug_assert!(q.base[q.size..].iter().all(|&d| d == 0));
- debug_assert!(r.base[r.size..].iter().all(|&d| d == 0));
-}
 }
 
 implcrate::cmp::PartialEqfor $name {

library/coretests/tests/num/bignum.rs

@@ -167,25 +167,6 @@ fn test_div_rem_small() {
 );
 }
 
-#[test]
-fntest_div_rem(){
-fndiv_rem(n:u64,d:u64) -> (Big,Big){
-letmut q = Big::from_small(42);
-letmut r = Big::from_small(42);
-Big::from_u64(n).div_rem(&Big::from_u64(d),&mut q,&mut r);
-(q, r)
-}
-assert_eq!(div_rem(1,1),(Big::from_small(1),Big::from_small(0)));
-assert_eq!(div_rem(4,3),(Big::from_small(1),Big::from_small(1)));
-assert_eq!(div_rem(1,7),(Big::from_small(0),Big::from_small(1)));
-assert_eq!(div_rem(45,9),(Big::from_small(5),Big::from_small(0)));
-assert_eq!(div_rem(103,9),(Big::from_small(11),Big::from_small(4)));
-assert_eq!(div_rem(123456,77),(Big::from_u64(1603),Big::from_small(25)));
-assert_eq!(div_rem(0xffff,1),(Big::from_u64(0xffff),Big::from_small(0)));
-assert_eq!(div_rem(0xeeee,0xffff),(Big::from_small(0),Big::from_u64(0xeeee)));
-assert_eq!(div_rem(2_000_000,2),(Big::from_u64(1_000_000),Big::from_u64(0)));
-}
-
 #[test]
 fntest_is_zero(){
 assert!(Big::from_small(0).is_zero());