Bigint.Mag.kmul: def of bend-kit-bignum@0.1.0.0
Import: import bend-kit-bignum@0.1.0.0/bigint.bend as Bigint
Lines 172-187 of bend-kit-bignum@0.1.0.0/bigint.bend: https://jend.leeeet.dev/read.txt?path=bend-kit-bignum@0.1.0.0/bigint.bend&start_line=172&end_line=187

import Base

# Karatsuba while both sides have at least 32 limbs, schoolbook below. f caps
# the depth; 32 halvings outrun any list that fits in memory.
def Mag.kmul(+f: Nat, +a: List<&2, U32>, +b: List<&2, U32>) -> List<&2, U32>:
  match f:
    case 0n:
      Mag.school(a, b)
    case 1n+p:
      +k = Nat.div(Nat.min(Mag.len(a), Mag.len(b)), 2n)
      +a0 = Mag.lo(a, k)
      +a1 = List.drop(&2, U32, a, k)
      +b0 = Mag.lo(b, k)
      +b1 = List.drop(&2, U32, b, k)
      Mag.if(List<&2, U32>, Nat.is_lt(k, 16n),
        u => Mag.school(a, b),
        u => Mag.kara(k, Mag.kmul(p, a0, b0), Mag.kmul(p, a1, b1),
          Mag.kmul(p, Mag.add(a0, a1, 0), Mag.add(b0, b1, 0))))

Uses (13):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.drop
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.div
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.is_lt
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.min
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32
  https://jend.leeeet.dev/definition.txt?path=bend-kit-bignum@0.1.0.0/bigint.bend&name=Mag.add
  https://jend.leeeet.dev/definition.txt?path=bend-kit-bignum@0.1.0.0/bigint.bend&name=Mag.if
  https://jend.leeeet.dev/definition.txt?path=bend-kit-bignum@0.1.0.0/bigint.bend&name=Mag.kara
  https://jend.leeeet.dev/definition.txt?path=bend-kit-bignum@0.1.0.0/bigint.bend&name=Mag.len
  https://jend.leeeet.dev/definition.txt?path=bend-kit-bignum@0.1.0.0/bigint.bend&name=Mag.lo
  https://jend.leeeet.dev/definition.txt?path=bend-kit-bignum@0.1.0.0/bigint.bend&name=Mag.school