1	# bend-osdev-acpi, fields.bend (internal): little-endian field readers for
2	# table parsers, over bytes whose length the parser has already checked. A
3	# field past the end reads as zero; every parser checks a table's length
4	# before reading the fields that length must hold.
5	import Base
6	import bend-osdev-word64@0.1.1.1/word64.bend as W
7	import bend-osdev-bytes@0.1.1.1/bytes.bend as B
8	
9	def AcpiF.u8(o: B.Octets, i: Nat) -> U32:
10	  Maybe.default(&2, U32, B.Octets.at(o, i), 0)
11	
12	def AcpiF.u16(o: B.Octets, +i: Nat) -> U32:
13	  Maybe.default(&2, U32, B.Octets.le16_at(o, i), 0)
14	
15	def AcpiF.u32(o: B.Octets, +i: Nat) -> U32:
16	  Maybe.default(&2, U32, B.Octets.le32_at(o, i), 0)
17	
18	def AcpiF.u64(o: B.Octets, +i: Nat) -> W.W64:
19	  Maybe.default(&2, W.W64, B.Octets.le64_at(o, i), W.W64.zero())
20	
21	# the 3-byte little-endian field at offset i
22	def AcpiF.u24(+o: B.Octets, +i: Nat) -> U32:
23	  U32.or(AcpiF.u16(o, i), U32.shln(AcpiF.u8(o, Nat.add(i, 2n)), 16n))
24	
25	# n bytes at offset i (fewer if o ends first)
26	def AcpiF.bytes(o: B.Octets, +i: Nat, n: Nat) -> B.Octets:
27	  B.Octets.slice(i, n, o)
28	
29	# bit k of a word
30	def AcpiF.bit(+v: U32, k: Nat) -> Bool:
31	  U32.is_eq(U32.and(U32.shrn(v, k), 1), 1)
32	
33	# bits k .. k + n - 1 of a word
34	def AcpiF.bits(+v: U32, k: Nat, n: Nat) -> U32:
35	  U32.and(U32.shrn(v, k), U32.sub(U32.shln(1, n), 1))
36	
37	# one byte, as Octets
38	def AcpiF.byte(v: U32) -> B.Octets:
39	  B.Octets.of_list([v])
40	
41	def AcpiF.le16(v: U32) -> B.Octets:
42	  B.Octets.le16(v)
43	
44	def AcpiF.le32(v: U32) -> B.Octets:
45	  B.Octets.le32(v)
46	
47	def AcpiF.le64(v: W.W64) -> B.Octets:
48	  B.Octets.le64(v)
49	
50	# the 3-byte little-endian encoding of the low 24 bits of v
51	def AcpiF.le24(+v: U32) -> B.Octets:
52	  B.Octets.of_list([v, U32.shrn(v, 8n), U32.shrn(v, 16n)])
53	
54	# o cut or padded with zeros to exactly n bytes
55	def AcpiF.fit(+n: Nat, +o: B.Octets) -> B.Octets:
56	  +h = B.Octets.take(n, o)
57	  B.Octets.append(h, B.Octets.zeros(Nat.sub(n, B.Octets.len(h))))