Chacha8rand.quarter: def of bend-collections-laws-crypto@1.0.0.0
Import: import bend-collections-laws-crypto@1.0.0.0/spec/math/random/chacha8rand.bend as Chacha8rand
Lines 58-69 of bend-collections-laws-crypto@1.0.0.0/spec/math/random/chacha8rand.bend: https://jend.leeeet.dev/read.txt?path=bend-collections-laws-crypto@1.0.0.0/spec/math/random/chacha8rand.bend&start_line=58&end_line=69

import Base

# RFC 8439 2.1: a += b; d ^= a; d <<<= 16; c += d; b ^= c; b <<<= 12;
# a += b; d ^= a; d <<<= 8; c += d; b ^= c; b <<<= 7 (2.2: on x[a..d])
def quarter(+x: List<&2, U32>, +a: Nat, +b: Nat, +c: Nat, +d: Nat) -> List<&2, U32>:
  +a1 = U32.add(get(x, a), get(x, b))
  +d1 = rotl(U32.xor(get(x, d), a1), 16n)
  +c1 = U32.add(get(x, c), d1)
  +b1 = rotl(U32.xor(get(x, b), c1), 12n)
  +a2 = U32.add(a1, b1)
  +d2 = rotl(U32.xor(d1, a2), 8n)
  +c2 = U32.add(c1, d2)
  +b2 = rotl(U32.xor(b1, c2), 7n)
  put(put(put(put(x, a, a2), b, b2), c, c2), d, d2)

Uses (8):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.add
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.xor
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/spec/math/random/chacha8rand.bend&name=get
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/spec/math/random/chacha8rand.bend&name=put
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/spec/math/random/chacha8rand.bend&name=rotl