Sha512.length_field: def of bend-collections-laws-crypto@1.0.0.0
Import: import bend-collections-laws-crypto@1.0.0.0/spec/crypto/sha512.bend as Sha512
Lines 149-154 of bend-collections-laws-crypto@1.0.0.0/spec/crypto/sha512.bend: https://jend.leeeet.dev/read.txt?path=bend-collections-laws-crypto@1.0.0.0/spec/crypto/sha512.bend&start_line=149&end_line=154

import Base

# The 128-bit block of the message length in bits, 8n: its low octet is
# 8 * (n mod 32) and the fifteen above it are n div 32 in base 256
# (8n = 256 * (n div 32) + 8 * (n mod 32)), so no Nat above n is formed.
def length_field(+n: Nat) -> List<&2, U32>:
  List.append(&2, U32, octets(15n, Nat.div(n, 32n)),
    [U32.shln(U32.from_nat(Nat.mod(n, 32n)), 3n)])

Uses (9):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.append
  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.mod
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.from_nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.shln
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/spec/crypto/sha512.bend&name=octets