Chacha.quarter: def of bend-collections@1.0.0.0
Import: import bend-collections@1.0.0.0/spec/crypto/chacha.bend as Chacha
Lines 38-52 of bend-collections@1.0.0.0/spec/crypto/chacha.bend: https://jend.leeeet.dev/read.txt?path=bend-collections@1.0.0.0/spec/crypto/chacha.bend&start_line=38&end_line=52

import Base

# 2.2: QUARTERROUND(a, b, c, d) applied to the state at those positions:
#   a += b; d ^= a; d <<<= 16;
#   c += d; b ^= c; b <<<= 12;
#   a += b; d ^= a; d <<<= 8;
#   c += d; b ^= c; b <<<= 7;
def quarter(+s: List<&2, U32>, +a: Nat, +b: Nat, +c: Nat, +d: Nat) -> List<&2, U32>:
  +a1 = U32.add(get(s, a), get(s, b))
  +d1 = rotl(U32.xor(get(s, d), a1), 16n)
  +c1 = U32.add(get(s, c), d1)
  +b1 = rotl(U32.xor(get(s, 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(s, 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@1.0.0.0/spec/crypto/chacha.bend&name=get
  https://jend.leeeet.dev/definition.txt?path=bend-collections@1.0.0.0/spec/crypto/chacha.bend&name=put
  https://jend.leeeet.dev/definition.txt?path=bend-collections@1.0.0.0/spec/crypto/chacha.bend&name=rotl