1	import Base
2	
3	def hex_digit_if(x: U32, small: Bool) -> Char:
4	  match small:
5	    case True{}:
6	      Chr{(48 + x : U32)}
7	    case False{}:
8	      Chr{(87 + x : U32)}
9	
10	def hex_digit(+x: U32) -> Char:
11	  hex_digit_if(x, U32.is_lt(x, 10))
12	
13	def hex_byte(+x: U32) -> String:
14	  SCon{hex_digit(U32.shrn(x,4n)),SCon{hex_digit(U32.and(x,15)),SNil{}}}
15	
16	def hex_word(+x: U32) -> String:
17	  hex_byte(U32.and(x,255)) ++ hex_byte(U32.and(U32.shrn(x,8n),255)) ++ hex_byte(U32.and(U32.shrn(x,16n),255)) ++ hex_byte(U32.shrn(x,24n))
18	
19	def hex_walk(n: Nat, +index: U32, pair: Array<U32> & U32) -> String:
20	  match n pair:
21	    case 0n Tuple{a,w}: hex_word(w)
22	    case 1n+p Tuple{a,w}: hex_word(w) ++ hex_walk(p,U32.inc(index),Array.get(U32,a,index))
23	
24	# The digest words as lowercase hex, bytes in little-endian word order.
25	def hex(a: Array<U32>) -> String:
26	  hex_walk(7n,1,Array.get(U32,a,0))