1	# Byte buffers packed four bytes to a U32, with bounds-checked access. Source: https://github.com/paymog/bend-kit/tree/main/bytes
2	import Base
3	# bend-kit-int@0.2.0.0
4	import 0x4eed9d7ac6ece61523d747a9d804e4f0/int.bend as Int
5	
6	# Bytes{len, buf}: byte i is bits 8*(i%4) of buf[i/4]. buf has the fewest 2^d words
7	# that hold len bytes. Every byte at or past len is 0, so equal buffers have equal words.
8	# Out-of-range reads answer None and out-of-range writes do nothing; Array alone would wrap.
9	#   import ./bytes/bytes.bend as Bytes
10	
11	type Bytes is Type:
12	  Bytes{len: U32, buf: Array<U32>}
13	
14	def b8(+x: U32) -> U32:
15	  (x .&. 255 : U32)
16	
17	def shift(+i: U32) -> Nat:
18	  U32.to_nat(((i .&. 3 : U32) * 8 : U32))
19	
20	def words(+n: U32) -> U32:
21	  ((n + 3 : U32) >> 2n : U32)
22	
23	# The fewest d with 2^d >= w.
24	def depth.go(f: Nat, more: Bool, +w: U32, +d: Nat, +cap: U32) -> Nat:
25	  match f:
26	    case 0n:
27	      d
28	    case 1n+p:
29	      match more:
30	        case False{}:
31	          d
32	        case True{}:
33	          depth.go(p, U32.is_lt((cap * 2 : U32), w), w, 1n+d, (cap * 2 : U32))
34	
35	def depth(+w: U32) -> Nat:
36	  depth.go(32n, U32.is_lt(1, w), w, 0n, 1)
37	
38	def alloc(+n: U32) -> Array<U32>:
39	  Array.new(U32, depth(words(n)), 0)
40	
41	# Unchecked byte read and write. Callers keep i below len.
42	def peek.of(+sh: Nat, r: Array<U32> & U32) -> Array<U32> & U32:
43	  (a, w) = r
44	  (a, b8(U32.shrn(w, sh)))
45	
46	def peek(a: Array<U32>, +i: U32) -> Array<U32> & U32:
47	  peek.of(shift(i), Array.get(U32, a, (i >> 2n : U32)))
48	
49	def poke.of(+i: U32, +v: U32, r: Array<U32> & U32) -> Array<U32>:
50	  (a, w) = r
51	  +sh = shift(i)
52	  Array.set(U32, a, (i >> 2n : U32), ((w .&. ((255 << sh) .^. 4294967295)) .|. (b8(v) << sh) : U32))
53	
54	def poke(a: Array<U32>, +i: U32, +v: U32) -> Array<U32>:
55	  poke.of(i, v, Array.get(U32, a, (i >> 2n : U32)))
56	
57	# n bytes from src[s..] to dst[d..], one byte at a time.
58	def copy.go(n: Nat, r: Array<U32> & U32, dst: Array<U32>, +s: U32, +d: U32) -> Array<U32> & Array<U32>:
59	  match n:
60	    case 0n:
61	      (a, v) = r
62	      (a, dst)
63	    case 1n+p:
64	      (a, v) = r
65	      copy.go(p, peek(a, (s + 1 : U32)), poke(dst, d, v), (s + 1 : U32), (d + 1 : U32))
66	
67	def copy.bytes(+m: U32, src: Array<U32>, dst: Array<U32>, +s: U32, +d: U32) -> Array<U32> & Array<U32>:
68	  copy.go(U32.to_nat(m), peek(src, s), dst, s, d)
69	
70	# n words from src[s..] to dst[d..] (word indexes).
71	def copy.words(n: Nat, r: Array<U32> & U32, dst: Array<U32>, +s: U32, +d: U32) -> Array<U32> & Array<U32>:
72	  match n:
73	    case 0n:
74	      (a, w) = r
75	      (a, dst)
76	    case 1n+p:
77	      (a, +w) = r
78	      copy.words(p, Array.get(U32, a, (s + 1 : U32)), Array.set(U32, dst, d, w), (s + 1 : U32), (d + 1 : U32))
79	
80	# m bytes to a word-aligned d from an unaligned s: each out word joins two source words.
81	# lo = 8*(s%4) and hi = 32 - lo; r holds source word k, prev the word before it.
82	def copy.shift(n: Nat, +lo: Nat, +hi: Nat, +prev: U32, r: Array<U32> & U32, dst: Array<U32>, +k: U32, +d: U32) -> Array<U32> & Array<U32>:
83	  match n:
84	    case 0n:
85	      (a, w) = r
86	      (a, dst)
87	    case 1n+p:
88	      (a, +w) = r
89	      copy.shift(p, lo, hi, w, Array.get(U32, a, (k + 1 : U32)), Array.set(U32, dst, d, (U32.shrn(prev, lo) .|. U32.shln(w, hi) : U32)), (k + 1 : U32), (d + 1 : U32))
90	
91	def copy.shift.at(+w: U32, +lo: U32, +k: U32, +d: U32, r: Array<U32> & U32, dst: Array<U32>) -> Array<U32> & Array<U32>:
92	  (a, prev) = r
93	  copy.shift(U32.to_nat(w), U32.to_nat(lo), U32.to_nat((32 - lo : U32)), prev, Array.get(U32, a, (k + 1 : U32)), dst, (k + 1 : U32), d)
94	
95	def copy.tail(+m: U32, +s: U32, +d: U32, r: Array<U32> & Array<U32>) -> Array<U32> & Array<U32>:
96	  (a, b) = r
97	  copy.bytes(m, a, b, s, d)
98	
99	def copy.pick(aligned: Bool, +m: U32, src: Array<U32>, dst: Array<U32>, +s: U32, +d: U32) -> Array<U32> & Array<U32>:
100	  match aligned:
101	    case True{}:
102	      +w = (m >> 2n : U32)
103	      +k = (w * 4 : U32)
104	      copy.tail((m - k : U32), (s + k : U32), (d + k : U32), copy.words(U32.to_nat(w), Array.get(U32, src, (s >> 2n : U32)), dst, (s >> 2n : U32), (d >> 2n : U32)))
105	    case False{}:
106	      +w = (m >> 2n : U32)
107	      +k = (w * 4 : U32)
108	      copy.tail((m - k : U32), (s + k : U32), (d + k : U32), copy.shift.at(w, ((s .&. 3 : U32) * 8 : U32), (s >> 2n : U32), (d >> 2n : U32), Array.get(U32, src, (s >> 2n : U32)), dst))
109	
110	def copy.dst(daligned: Bool, +m: U32, src: Array<U32>, dst: Array<U32>, +s: U32, +d: U32) -> Array<U32> & Array<U32>:
111	  match daligned:
112	    case False{}:
113	      copy.bytes(m, src, dst, s, d)
114	    case True{}:
115	      copy.pick(U32.is_eq((s .&. 3 : U32), 0), m, src, dst, s, d)
116	
117	# m bytes from src[s..] to dst[d..]. Whole words when d is word-aligned, shifted when s is not.
118	# ponytail: an unaligned d (append after an odd length) copies bytes; merge into d's first word if that gets hot.
119	def copy(+m: U32, src: Array<U32>, dst: Array<U32>, +s: U32, +d: U32) -> Array<U32> & Array<U32>:
120	  copy.dst(U32.is_eq((d .&. 3 : U32), 0), m, src, dst, s, d)
121	
122	# n zero bytes.
123	def new(+n: U32) -> Bytes:
124	  Bytes{n, alloc(n)}
125	
126	def length(b: Bytes) -> Bytes & U32:
127	  Bytes{+len, buf} = b
128	  (Bytes{len, buf}, len)
129	
130	def get.some(+len: U32, r: Array<U32> & U32) -> Bytes & Maybe<&2, U32>:
131	  (a, v) = r
132	  (Bytes{len, a}, Some{v})
133	
134	def get.if(ok: Bool, +len: U32, buf: Array<U32>, +i: U32) -> Bytes & Maybe<&2, U32>:
135	  match ok:
136	    case True{}:
137	      get.some(len, peek(buf, i))
138	    case False{}:
139	      (Bytes{len, buf}, None{})
140	
141	# Byte i, or None when i >= len.
142	def get(b: Bytes, +i: U32) -> Bytes & Maybe<&2, U32>:
143	  Bytes{+len, buf} = b
144	  get.if(U32.is_lt(i, len), len, buf, i)
145	
146	def set.if(ok: Bool, +len: U32, buf: Array<U32>, +i: U32, +v: U32) -> Bytes:
147	  match ok:
148	    case True{}:
149	      Bytes{len, poke(buf, i, v)}
150	    case False{}:
151	      Bytes{len, buf}
152	
153	# Byte i becomes v & 255. Nothing changes when i >= len.
154	def set(b: Bytes, +i: U32, +v: U32) -> Bytes:
155	  Bytes{+len, buf} = b
156	  set.if(U32.is_lt(i, len), len, buf, i, v)
157	
158	# The next index: one forward when up, one back when not.
159	def step(+up: Bool, +i: U32) -> U32:
160	  Bool.pick(U32, up, (i + 1 : U32), (i - 1 : U32))
161	
162	# Do n bytes from i fit in len?
163	def fits(+len: U32, +i: U32, +n: U32) -> Bool:
164	  Bool.and(U32.is_le(n, len), U32.is_le(i, (len - n : U32)))
165	
166	# n bytes from j, each shifted in below the ones before: the first byte read is the most significant.
167	def uint.go(n: Nat, r: Array<U32> & U32, +j: U32, +up: Bool, +acc: U32) -> Array<U32> & U32:
168	  match n:
169	    case 0n:
170	      (a, v) = r
171	      (a, acc)
172	    case 1n+p:
173	      (a, +v) = r
174	      uint.go(p, peek(a, step(up, j)), step(up, j), up, ((acc << 8n) .|. v : U32))
175	
176	# Big-endian reads forward from i; little-endian reads back from the last byte.
177	def uint.if(ok: Bool, +len: U32, buf: Array<U32>, +i: U32, +n: U32, +be: Bool) -> Bytes & Maybe<&2, U32>:
178	  match ok:
179	    case True{}:
180	      +j = Bool.pick(U32, be, i, (i + n - 1 : U32))
181	      get.some(len, uint.go(U32.to_nat(n), peek(buf, j), j, be, 0))
182	    case False{}:
183	      (Bytes{len, buf}, None{})
184	
185	def uint(b: Bytes, +i: U32, +n: U32, +be: Bool) -> Bytes & Maybe<&2, U32>:
186	  Bytes{+len, buf} = b
187	  uint.if(fits(len, i, n), len, buf, i, n, be)
188	
189	# Unsigned integers at byte i, or None when they run past len.
190	# be: most significant byte first (network order); le: least significant first.
191	def get.u16be(b: Bytes, +i: U32) -> Bytes & Maybe<&2, U32>:
192	  uint(b, i, 2, True{})
193	
194	def get.u16le(b: Bytes, +i: U32) -> Bytes & Maybe<&2, U32>:
195	  uint(b, i, 2, False{})
196	
197	def get.u32be(b: Bytes, +i: U32) -> Bytes & Maybe<&2, U32>:
198	  uint(b, i, 4, True{})
199	
200	def get.u32le(b: Bytes, +i: U32) -> Bytes & Maybe<&2, U32>:
201	  uint(b, i, 4, False{})
202	
203	# n bytes of v from j, least significant first.
204	def put.go(n: Nat, a: Array<U32>, +j: U32, +up: Bool, +v: U32) -> Array<U32>:
205	  match n:
206	    case 0n:
207	      a
208	    case 1n+p:
209	      put.go(p, poke(a, j, v), step(up, j), up, U32.shrn(v, 8n))
210	
211	# Little-endian writes forward from i; big-endian writes back from the last byte.
212	def put.if(ok: Bool, +len: U32, buf: Array<U32>, +i: U32, +n: U32, +be: Bool, +v: U32) -> Bytes:
213	  match ok:
214	    case True{}:
215	      Bytes{len, put.go(U32.to_nat(n), buf, Bool.pick(U32, be, (i + n - 1 : U32), i), Bool.not(be), v)}
216	    case False{}:
217	      Bytes{len, buf}
218	
219	def put(b: Bytes, +i: U32, +n: U32, +be: Bool, +v: U32) -> Bytes:
220	  Bytes{+len, buf} = b
221	  put.if(fits(len, i, n), len, buf, i, n, be, v)
222	
223	# v's low 16 or 32 bits at byte i. Nothing changes when they would run past len.
224	def set.u16be(b: Bytes, +i: U32, +v: U32) -> Bytes:
225	  put(b, i, 2, True{}, v)
226	
227	def set.u16le(b: Bytes, +i: U32, +v: U32) -> Bytes:
228	  put(b, i, 2, False{}, v)
229	
230	def set.u32be(b: Bytes, +i: U32, +v: U32) -> Bytes:
231	  put(b, i, 4, True{}, v)
232	
233	def set.u32le(b: Bytes, +i: U32, +v: U32) -> Bytes:
234	  put(b, i, 4, False{}, v)
235	
236	# The U64 whose words, in byte order, are x then y.
237	def u64.of(be: Bool, +x: U32, +y: U32) -> Int.U64:
238	  match be:
239	    case True{}:
240	      Int.U64.or(Int.U64.shl(Int.U64.from_u32(x), 32n), Int.U64.from_u32(y))
241	    case False{}:
242	      Int.U64.or(Int.U64.shl(Int.U64.from_u32(y), 32n), Int.U64.from_u32(x))
243	
244	def u64.join(+be: Bool, x: Maybe<&2, U32>, y: Maybe<&2, U32>) -> Maybe<&2, Int.U64>:
245	  match x y:
246	    case Some{a} Some{c}:
247	      Some{u64.of(be, a, c)}
248	    case _ _:
249	      None{}
250	
251	def u64.lo(+be: Bool, x: Maybe<&2, U32>, r: Bytes & Maybe<&2, U32>) -> Bytes & Maybe<&2, Int.U64>:
252	  (b, y) = r
253	  (b, u64.join(be, x, y))
254	
255	def u64.hi(+i: U32, +be: Bool, r: Bytes & Maybe<&2, U32>) -> Bytes & Maybe<&2, Int.U64>:
256	  (b, x) = r
257	  u64.lo(be, x, uint(b, (i + 4 : U32), 4, be))
258	
259	def u64(b: Bytes, +i: U32, +be: Bool) -> Bytes & Maybe<&2, Int.U64>:
260	  u64.hi(i, be, uint(b, i, 4, be))
261	
262	# A U64 at byte i, or None when its 8 bytes run past len.
263	def get.u64be(b: Bytes, +i: U32) -> Bytes & Maybe<&2, Int.U64>:
264	  u64(b, i, True{})
265	
266	def get.u64le(b: Bytes, +i: U32) -> Bytes & Maybe<&2, Int.U64>:
267	  u64(b, i, False{})
268	
269	# Writes words x then y at byte i, both in the same byte order.
270	def put64.if(ok: Bool, +len: U32, buf: Array<U32>, +i: U32, +be: Bool, +x: U32, +y: U32) -> Bytes:
271	  match ok:
272	    case True{}:
273	      put(put(Bytes{len, buf}, i, 4, be, x), (i + 4 : U32), 4, be, y)
274	    case False{}:
275	      Bytes{len, buf}
276	
277	def put64(b: Bytes, +i: U32, +be: Bool, +v: Int.U64) -> Bytes:
278	  Bytes{+len, buf} = b
279	  +hi = Int.U64.to_u32(Int.U64.shr(v, 32n))
280	  +lo = Int.U64.to_u32(v)
281	  put64.if(fits(len, i, 8), len, buf, i, be, Bool.pick(U32, be, hi, lo), Bool.pick(U32, be, lo, hi))
282	
283	# v at byte i. Nothing changes when its 8 bytes would run past len.
284	def set.u64be(b: Bytes, +i: U32, +v: Int.U64) -> Bytes:
285	  put64(b, i, True{}, v)
286	
287	def set.u64le(b: Bytes, +i: U32, +v: Int.U64) -> Bytes:
288	  put64(b, i, False{}, v)
289	
290	# String.length counts in Nat, which costs more than the walk itself.
291	def count(s: String, +n: U32) -> U32:
292	  match s:
293	    case SNil{}:
294	      n
295	    case SCon{c, t}:
296	      count(t, (n + 1 : U32))
297	
298	# Bytes enter at the top of w and shift down, so a full word has byte 0 lowest.
299	def flush(full: Bool, a: Array<U32>, +k: U32, +w: U32) -> Array<U32>:
300	  match full:
301	    case True{}:
302	      Array.set(U32, a, k, w)
303	    case False{}:
304	      a
305	
306	def from.go(s: String, a: Array<U32>, +i: U32, +w: U32) -> Array<U32>:
307	  match s:
308	    case SNil{}:
309	      +r = (i .&. 3 : U32)
310	      flush(U32.is_ne(r, 0), a, (i >> 2n : U32), U32.shrn(w, U32.to_nat((((4 - r) .&. 3) * 8 : U32))))
311	    case SCon{Chr{+c}, t}:
312	      +w2 = ((w >> 8n) .|. (b8(c) << 24n) : U32)
313	      +full = U32.is_eq((i .&. 3 : U32), 3)
314	      from.go(t, flush(full, a, (i >> 2n : U32), w2), (i + 1 : U32), Bool.pick(U32, full, 0, w2))
315	
316	# A byte string (one Char per octet, as Wire and Http use) to Bytes. Each Char keeps its low 8 bits.
317	def from_string(+s: String) -> Bytes:
318	  +n = count(s, 0)
319	  Bytes{n, from.go(s, alloc(n), 0, 0)}
320	
321	def to.go(n: Nat, r: Array<U32> & U32, +i: U32, acc: String) -> String:
322	  match n:
323	    case 0n:
324	      acc
325	    case 1n+p:
326	      (a, v) = r
327	      to.go(p, peek(a, (i - 1 : U32)), (i - 1 : U32), SCon{Chr{v}, acc})
328	
329	# Bytes to a byte string, one Char per octet.
330	def to_string(b: Bytes) -> String:
331	  Bytes{+len, buf} = b
332	  to.go(U32.to_nat(len), peek(buf, (len - 1 : U32)), (len - 1 : U32), SNil{})
333	
334	def slice.fin(+len: U32, +m: U32, r: Array<U32> & Array<U32>) -> Bytes & Bytes:
335	  (a, c) = r
336	  (Bytes{len, a}, Bytes{m, c})
337	
338	def slice.at(+len: U32, buf: Array<U32>, +s: U32, +m: U32) -> Bytes & Bytes:
339	  slice.fin(len, m, copy(m, buf, alloc(m), s, 0))
340	
341	# The buffer back, and a copy of up to n bytes from start. Both ends are clamped to len.
342	def slice(b: Bytes, +start: U32, +n: U32) -> Bytes & Bytes:
343	  Bytes{+len, buf} = b
344	  +s = U32.min(start, len)
345	  slice.at(len, buf, s, U32.min(n, (len - s : U32)))
346	
347	def dst(r: Array<U32> & Array<U32>) -> Array<U32>:
348	  (src, out) = r
349	  out
350	
351	# Does a buffer holding len bytes have room for n? Its 2^d words fit the fewest that hold len.
352	def room(+len: U32, +n: U32) -> Bool:
353	  U32.is_le(words(n), U32.shln(1, depth(words(len))))
354	
355	def grow.if(fits: Bool, +len: U32, buf: Array<U32>, +n: U32) -> Array<U32>:
356	  match fits:
357	    case True{}:
358	      buf
359	    case False{}:
360	      dst(copy(len, buf, alloc(n), 0, 0))
361	
362	# buf, or a copy of its first len bytes in the fewest 2^d words that hold n.
363	def grow(+len: U32, buf: Array<U32>, +n: U32) -> Array<U32>:
364	  grow.if(room(len, n), len, buf, n)
365	
366	# a then b. b is written into a's buffer while it has room, and the buffer at least
367	# doubles when it runs out, so building a buffer one piece at a time is O(total).
368	def append(a: Bytes, b: Bytes) -> Bytes:
369	  Bytes{+la, ba} = a
370	  Bytes{+lb, bb} = b
371	  +n = (la + lb : U32)
372	  Bytes{n, dst(copy(lb, bb, grow(la, ba, n), 0, la))}
373	
374	def concat.total.con(x: Bytes, r: List<&1, Bytes> & U32) -> List<&1, Bytes> & U32:
375	  (t, n) = r
376	  (Con{x, t}, n)
377	
378	def concat.total(xs: List<&1, Bytes>, +n: U32) -> List<&1, Bytes> & U32:
379	  match xs:
380	    case Nil{}:
381	      (Nil{}, n)
382	    case Con{x, t}:
383	      Bytes{+l, buf} = x
384	      concat.total.con(Bytes{l, buf}, concat.total(t, (n + l : U32)))
385	
386	def concat.go(xs: List<&1, Bytes>, out: Array<U32>, +at: U32) -> Array<U32>:
387	  match xs:
388	    case Nil{}:
389	      out
390	    case Con{x, t}:
391	      Bytes{+l, buf} = x
392	      concat.go(t, dst(copy(l, buf, out, 0, at)), (at + l : U32))
393	
394	def concat.of(r: List<&1, Bytes> & U32) -> Bytes:
395	  (xs, +n) = r
396	  Bytes{n, concat.go(xs, alloc(n), 0)}
397	
398	# The pieces in order, in one new buffer: one copy per byte, however many pieces.
399	def concat(xs: List<&1, Bytes>) -> Bytes:
400	  concat.of(concat.total(xs, 0))
401	
402	# Does needle match at j? ok is the previous byte's result; the first mismatch stops the walk.
403	def at.go(needle: String, ok: Bool, r: Array<U32> & U32, +j: U32) -> Array<U32> & Bool:
404	  match needle:
405	    case SNil{}:
406	      (a, v) = r
407	      (a, ok)
408	    case SCon{Chr{+c}, t}:
409	      match ok:
410	        case False{}:
411	          (a, v) = r
412	          (a, False{})
413	        case True{}:
414	          (a, +v) = r
415	          at.go(t, U32.is_eq(v, c), peek(a, (j + 1 : U32)), (j + 1 : U32))
416	
417	def at(a: Array<U32>, +needle: String, +j: U32) -> Array<U32> & Bool:
418	  at.go(needle, True{}, peek(a, j), j)
419	
420	# ponytail: naive search; a mismatch costs one byte read per position, but a repetitive needle is O(len * needle). Add a SWAR scan or two-way search if find gets hot.
421	# f counts the positions left after i.
422	def find.go(f: Nat, r: Array<U32> & Bool, +needle: String, +i: U32, +up: Bool) -> Array<U32> & Maybe<&2, U32>:
423	  match f:
424	    case 0n:
425	      (a, hit) = r
426	      (a, Bool.pick(Maybe<&2, U32>, hit, Some{i}, None{}))
427	    case 1n+p:
428	      (a, hit) = r
429	      match hit:
430	        case True{}:
431	          (a, Some{i})
432	        case False{}:
433	          find.go(p, at(a, needle, step(up, i)), needle, step(up, i), up)
434	
435	def find.fin(+len: U32, r: Array<U32> & Maybe<&2, U32>) -> Bytes & Maybe<&2, U32>:
436	  (a, x) = r
437	  (Bytes{len, a}, x)
438	
439	def find.at(none: Bool, +len: U32, buf: Array<U32>, +needle: String, +i: U32, +f: U32, +up: Bool) -> Bytes & Maybe<&2, U32>:
440	  match none:
441	    case True{}:
442	      (Bytes{len, buf}, None{})
443	    case False{}:
444	      find.fin(len, find.go(U32.to_nat(f), at(buf, needle, i), needle, i, up))
445	
446	# Index of the first match of needle (a byte string) at or after start, or None.
447	# An empty needle matches at start when start <= len.
448	def find.from(b: Bytes, +needle: String, +start: U32) -> Bytes & Maybe<&2, U32>:
449	  Bytes{+len, buf} = b
450	  +m = count(needle, 0)
451	  find.at(Bool.or(U32.is_lt(len, m), U32.is_lt((len - m : U32), start)), len, buf, needle, start, (len - m - start : U32), True{})
452	
453	# Index of the first match of needle (a byte string), or None. An empty needle matches at 0.
454	def find(b: Bytes, +needle: String) -> Bytes & Maybe<&2, U32>:
455	  find.from(b, needle, 0)
456	
457	# Index of the last match of needle, or None. An empty needle matches at len.
458	def rfind(b: Bytes, +needle: String) -> Bytes & Maybe<&2, U32>:
459	  Bytes{+len, buf} = b
460	  +m = count(needle, 0)
461	  find.at(U32.is_lt(len, m), len, buf, needle, (len - m : U32), (len - m : U32), False{})
462	
463	def at.fin(+len: U32, r: Array<U32> & Bool) -> Bytes & Bool:
464	  (a, ok) = r
465	  (Bytes{len, a}, ok)
466	
467	def at.if(fits: Bool, +len: U32, buf: Array<U32>, +needle: String, +j: U32) -> Bytes & Bool:
468	  match fits:
469	    case True{}:
470	      at.fin(len, at(buf, needle, j))
471	    case False{}:
472	      (Bytes{len, buf}, False{})
473	
474	# Does b begin with prefix (a byte string)?
475	def starts_with(b: Bytes, +prefix: String) -> Bytes & Bool:
476	  Bytes{+len, buf} = b
477	  +m = count(prefix, 0)
478	  at.if(U32.is_le(m, len), len, buf, prefix, 0)
479	
480	# Does b end with suffix (a byte string)?
481	def ends_with(b: Bytes, +suffix: String) -> Bytes & Bool:
482	  Bytes{+len, buf} = b
483	  +m = count(suffix, 0)
484	  at.if(U32.is_le(m, len), len, buf, suffix, (len - m : U32))
485	
486	# Match positions of sep, latest first, that do not overlap an earlier match.
487	# f counts the positions left; skip counts the bytes still inside the last match.
488	def split.scan(f: Nat, r: Array<U32> & Bool, +sep: String, +m: U32, +i: U32, +skip: U32, +cuts: List<&2, U32>) -> Array<U32> & List<&2, U32>:
489	  match f:
490	    case 0n:
491	      (a, hit) = r
492	      (a, cuts)
493	    case 1n+p:
494	      (a, +hit) = r
495	      +take = Bool.and(hit, U32.is_eq(skip, 0))
496	      +next = Bool.pick(U32, take, (m - 1 : U32), Bool.pick(U32, U32.is_eq(skip, 0), 0, (skip - 1 : U32)))
497	      split.scan(p, at(a, sep, (i + 1 : U32)), sep, m, (i + 1 : U32), next, Bool.pick(List<&2, U32>, take, Con{i, cuts}, cuts))
498	
499	def snd(r: Bytes & Bytes) -> Bytes:
500	  (a, b) = r
501	  b
502	
503	# r holds the buffer and the piece that ends at end; each earlier cut j starts one at j + m.
504	def split.cut(cuts: List<&2, U32>, r: Bytes & Bytes, +end: U32, +m: U32, acc: List<&1, Bytes>) -> List<&1, Bytes>:
505	  match cuts:
506	    case Nil{}:
507	      (b, piece) = r
508	      Con{snd(slice(b, 0, end)), Con{piece, acc}}
509	    case Con{+j, t}:
510	      (b, piece) = r
511	      split.cut(t, slice(b, (j + m : U32), (end - j - m : U32)), j, m, Con{piece, acc})
512	
513	def split.of(cuts: List<&2, U32>, b: Bytes, +len: U32, +m: U32) -> List<&1, Bytes>:
514	  match cuts:
515	    case Nil{}:
516	      Con{b, Nil{}}
517	    case Con{+j, t}:
518	      split.cut(t, slice(b, (j + m : U32), (len - j - m : U32)), j, m, Nil{})
519	
520	def split.run(+len: U32, +m: U32, r: Array<U32> & List<&2, U32>) -> List<&1, Bytes>:
521	  (a, cuts) = r
522	  split.of(cuts, Bytes{len, a}, len, m)
523	
524	def split.if(whole: Bool, +len: U32, buf: Array<U32>, +sep: String, +m: U32) -> List<&1, Bytes>:
525	  match whole:
526	    case True{}:
527	      Con{Bytes{len, buf}, Nil{}}
528	    case False{}:
529	      split.run(len, m, split.scan(U32.to_nat((len - m + 1 : U32)), at(buf, sep, 0), sep, m, 0, 0, Nil{}))
530	
531	# The pieces between matches of sep (a byte string), left to right. n matches give n + 1
532	# pieces, so a match at either end gives an empty piece. An empty sep gives b whole.
533	def split(b: Bytes, +sep: String) -> List<&1, Bytes>:
534	  Bytes{+len, buf} = b
535	  +m = count(sep, 0)
536	  split.if(Bool.or(U32.is_eq(m, 0), U32.is_lt(len, m)), len, buf, sep, m)
537	
538	# Compares whole words; same tells whether the previous pair matched.
539	def eq.go(n: Nat, same: Bool, r: Array<U32> & U32, s: Array<U32> & U32, +i: U32) -> Array<U32> & Array<U32> & Bool:
540	  match n:
541	    case 0n:
542	      (x, v) = r
543	      (y, w) = s
544	      (x, y, same)
545	    case 1n+p:
546	      match same:
547	        case False{}:
548	          (x, v) = r
549	          (y, w) = s
550	          (x, y, False{})
551	        case True{}:
552	          (x, +v) = r
553	          (y, +w) = s
554	          eq.go(p, U32.is_eq(v, w), Array.get(U32, x, (i + 1 : U32)), Array.get(U32, y, (i + 1 : U32)), (i + 1 : U32))
555	
556	def eq.fin(+la: U32, +lb: U32, r: Array<U32> & Array<U32> & Bool) -> Bytes & Bytes & Bool:
557	  (x, y, ok) = r
558	  (Bytes{la, x}, Bytes{lb, y}, ok)
559	
560	def eq.len(same: Bool, +la: U32, xa: Array<U32>, +lb: U32, ya: Array<U32>) -> Bytes & Bytes & Bool:
561	  match same:
562	    case False{}:
563	      (Bytes{la, xa}, Bytes{lb, ya}, False{})
564	    case True{}:
565	      eq.fin(la, lb, eq.go(U32.to_nat(words(la)), True{}, Array.get(U32, xa, 0), Array.get(U32, ya, 0), 0))
566	
567	# Both buffers back, and whether they hold the same bytes.
568	def eq(a: Bytes, b: Bytes) -> Bytes & Bytes & Bool:
569	  Bytes{+la, xa} = a
570	  Bytes{+lb, ya} = b
571	  eq.len(U32.is_eq(la, lb), la, xa, lb, ya)
572	
573	# Byte 0 of w becomes the most significant, so words compare in byte order.
574	def bswap(+w: U32) -> U32:
575	  ((b8(w) << 24n) .|. (b8(U32.shrn(w, 8n)) << 16n) .|. (b8(U32.shrn(w, 16n)) << 8n) .|. U32.shrn(w, 24n) : U32)
576	
577	# Compares whole words; c is the previous pair's order.
578	def cmp.go(n: Nat, c: Cmp, r: Array<U32> & U32, s: Array<U32> & U32, +i: U32) -> Array<U32> & Array<U32> & Cmp:
579	  match n:
580	    case 0n:
581	      (x, v) = r
582	      (y, w) = s
583	      (x, y, c)
584	    case 1n+p:
585	      match c:
586	        case LT{}:
587	          (x, v) = r
588	          (y, w) = s
589	          (x, y, LT{})
590	        case GT{}:
591	          (x, v) = r
592	          (y, w) = s
593	          (x, y, GT{})
594	        case EQ{}:
595	          (x, +v) = r
596	          (y, +w) = s
597	          cmp.go(p, U32.cmp(bswap(v), bswap(w)), Array.get(U32, x, (i + 1 : U32)), Array.get(U32, y, (i + 1 : U32)), (i + 1 : U32))
598	
599	def cmp.len(c: Cmp, +la: U32, +lb: U32) -> Cmp:
600	  match c:
601	    case EQ{}:
602	      U32.cmp(la, lb)
603	    case LT{}:
604	      LT{}
605	    case GT{}:
606	      GT{}
607	
608	def cmp.fin(+la: U32, +lb: U32, r: Array<U32> & Array<U32> & Cmp) -> Bytes & Bytes & Cmp:
609	  (x, y, c) = r
610	  (Bytes{la, x}, Bytes{lb, y}, cmp.len(c, la, lb))
611	
612	# Both buffers back, and their order byte by byte; a prefix sorts first.
613	# The shorter buffer's bytes past its len are 0, so its last word compares low when only the longer one goes on.
614	def cmp(a: Bytes, b: Bytes) -> Bytes & Bytes & Cmp:
615	  Bytes{+la, xa} = a
616	  Bytes{+lb, ya} = b
617	  cmp.fin(la, lb, cmp.go(U32.to_nat(words(U32.min(la, lb))), EQ{}, Array.get(U32, xa, 0), Array.get(U32, ya, 0), 0))
618	
619	def nibble(+n: U32) -> Char:
620	  Chr{Bool.pick(U32, U32.is_lt(n, 10), (48 + n : U32), (87 + n : U32))}
621	
622	def hex.go(n: Nat, r: Array<U32> & U32, +i: U32, acc: String) -> String:
623	  match n:
624	    case 0n:
625	      acc
626	    case 1n+p:
627	      (a, +v) = r
628	      hex.go(p, peek(a, (i - 1 : U32)), (i - 1 : U32), SCon{nibble(U32.shrn(v, 4n)), SCon{nibble((v .&. 15 : U32)), acc}})
629	
630	# Two lowercase hex digits per byte.
631	def to_hex(b: Bytes) -> String:
632	  Bytes{+len, buf} = b
633	  hex.go(U32.to_nat(len), peek(buf, (len - 1 : U32)), (len - 1 : U32), SNil{})
634	
635	def in(+lo: U32, +c: U32, +hi: U32) -> Bool:
636	  Bool.and(U32.is_le(lo, c), U32.is_le(c, hi))
637	
638	# A hex digit's value, or 16.
639	def unnibble(+c: U32) -> U32:
640	  Bool.pick(U32, in(48, c, 57), (c - 48 : U32), Bool.pick(U32, in(97, c, 102), (c - 87 : U32), Bool.pick(U32, in(65, c, 70), (c - 55 : U32), 16)))
641	
642	def poke.when(write: Bool, a: Array<U32>, +i: U32, +v: U32) -> Array<U32>:
643	  match write:
644	    case True{}:
645	      poke(a, i, v)
646	    case False{}:
647	      a
648	
649	# hi is the previous digit; an odd i completes a byte.
650	def unhex.go(s: String, a: Array<U32>, +i: U32, +hi: U32, +ok: Bool) -> Array<U32> & Bool:
651	  match s:
652	    case SNil{}:
653	      (a, ok)
654	    case SCon{Chr{+c}, t}:
655	      +d = unnibble(c)
656	      unhex.go(t, poke.when(U32.is_eq((i .&. 1 : U32), 1), a, (i >> 1n : U32), ((hi << 4n) .|. d : U32)), (i + 1 : U32), d, Bool.and(ok, U32.is_lt(d, 16)))
657	
658	def decoded(+n: U32, r: Array<U32> & Bool) -> Maybe<&1, Bytes>:
659	  (a, ok) = r
660	  match ok:
661	    case True{}:
662	      Some{Bytes{n, a}}
663	    case False{}:
664	      None{}
665	
666	def unhex.if(even: Bool, +s: String, +n: U32) -> Maybe<&1, Bytes>:
667	  match even:
668	    case True{}:
669	      decoded((n >> 1n : U32), unhex.go(s, alloc((n >> 1n : U32)), 0, 0, True{}))
670	    case False{}:
671	      None{}
672	
673	# Hex digits, either case, to bytes. None for an odd count or a non-hex char.
674	def from_hex(+s: String) -> Maybe<&1, Bytes>:
675	  +n = count(s, 0)
676	  unhex.if(U32.is_eq((n .&. 1 : U32), 0), s, n)
677	
678	# RFC 4648 §4: the standard alphabet, padded with '='.
679	def b64.char(+i: U32) -> U32:
680	  Bool.pick(U32, U32.is_lt(i, 26), (65 + i : U32), Bool.pick(U32, U32.is_lt(i, 52), (71 + i : U32), Bool.pick(U32, U32.is_lt(i, 62), (i - 4 : U32), Bool.pick(U32, U32.is_eq(i, 62), 43, 47))))
681	
682	# The six bits of v at k as a base64 char.
683	def b64.at(+v: U32, +k: Nat) -> Char:
684	  Chr{b64.char((U32.shrn(v, k) .&. 63 : U32))}
685	
686	# Groups of three bytes, last first; r holds the 24 bits of the group at i.
687	def b64.go(n: Nat, r: Array<U32> & U32, +i: U32, acc: String) -> String:
688	  match n:
689	    case 0n:
690	      acc
691	    case 1n+p:
692	      (a, +v) = r
693	      +j = (i - 3 : U32)
694	      b64.go(p, uint.go(3n, peek(a, j), j, True{}, 0), j, SCon{b64.at(v, 18n), SCon{b64.at(v, 12n), SCon{b64.at(v, 6n), SCon{b64.at(v, 0n), acc}}}})
695	
696	# The rem < 3 bytes after the last whole group, then the groups before them.
697	def b64.tail(+rem: U32, +t: U32, +q: U32, r: Array<U32> & U32) -> String:
698	  (a, +v0) = r
699	  +v = U32.shln(v0, U32.to_nat(((3 - rem) * 8 : U32)))
700	  +end = Bool.pick(String, U32.is_eq(rem, 0), "", Bool.pick(String, U32.is_eq(rem, 1), SCon{b64.at(v, 18n), SCon{b64.at(v, 12n), "=="}}, SCon{b64.at(v, 18n), SCon{b64.at(v, 12n), SCon{b64.at(v, 6n), "="}}}))