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// Copyright 2017 The Wuffs Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
pub status "#bad code"
pri status "#internal error: inconsistent I/O"
// TODO: move bulk data buffers like decoder.suffixes or decoder.output into
// the workbuf? The first attempt at this was a performance regression for
// decoding all but the smallest GIFs. See these git commits for numbers:
// - 49627b4 Flatten the lzw.decoder.suffixes array
// - f877fb2 Use the workbuf instead of lzw.decoder.suffixes
// - 85be5b9 Delete the obsolete lzw.decoder.suffixes array
// and the roll back has combined numbers:
// - 3056a84 Roll back 3 recent lzw.decoder.suffixes commits
pub const decoder_workbuf_len_max_incl_worst_case base.u64 = 0
pub struct decoder?(
// set_literal_width_arg is 1 plus the saved argument passed to
// set_literal_width. This is assigned to the literal_width field at the
// start of decode_io_writer. During that method, calling set_literal_width
// will change set_literal_width_arg but not literal_width.
set_literal_width_arg : base.u32[..= 9],
// read_from state that does not change during a decode call.
literal_width : base.u32[..= 8],
clear_code : base.u32[..= 256],
end_code : base.u32[..= 257],
// read_from state that does change during a decode call.
save_code : base.u32[..= 4096],
prev_code : base.u32[..= 4095],
width : base.u32[..= 12],
bits : base.u32,
n_bits : base.u32[..= 31],
output_ri : base.u32[..= 8191],
output_wi : base.u32[..= 8191],
// read_from return value. The read_from method effectively returns a
// base.u32 to show how decode should continue after calling write_to. That
// value needs to be saved across write_to's possible suspension, so we
// might as well save it explicitly as a decoder field.
read_from_return_value : base.u32,
// read_from per-code state.
prefixes : array[4096] base.u16[..= 4095],
util : base.utility,
)(
// read_from per-code state.
suffixes : array[4096] array[8] base.u8,
// lm1s is the "length minus 1"s of the values for the implicit key-value
// table in this decoder. See std/lzw/README.md for more detail.
lm1s : array[4096] base.u16,
// output[output_ri:output_wi] is the buffered output, connecting read_from
// with write_to and flush.
output : array[8192 + 7] base.u8,
)
pub func decoder.set_literal_width!(lw: base.u32[..= 8]) {
this.set_literal_width_arg = args.lw + 1
}
pub func decoder.workbuf_len() base.range_ii_u64 {
return this.util.make_range_ii_u64(min_incl: 0, max_incl: 0)
}
pub func decoder.decode_io_writer?(dst: base.io_writer, src: base.io_reader, workbuf: slice base.u8) {
var i : base.u32[..= 8191]
// Initialize read_from state.
this.literal_width = 8
if this.set_literal_width_arg > 0 {
this.literal_width = this.set_literal_width_arg - 1
}
this.clear_code = (1 as base.u32) << this.literal_width
this.end_code = this.clear_code + 1
this.save_code = this.end_code
this.prev_code = this.end_code
this.width = this.literal_width + 1
this.bits = 0
this.n_bits = 0
this.output_ri = 0
this.output_wi = 0
i = 0
while i < this.clear_code {
assert i < 256 via "a < b: a < c; c <= b"(c: this.clear_code)
this.lm1s[i] = 0
this.suffixes[i][0] = i as base.u8
i += 1
}
while true {
this.read_from!(src: args.src)
if this.output_wi > 0 {
this.write_to?(dst: args.dst)
}
if this.read_from_return_value == 0 {
break
} else if this.read_from_return_value == 1 {
continue
} else if this.read_from_return_value == 2 {
yield? base."$short read"
} else if this.read_from_return_value == 3 {
return "#bad code"
} else {
return "#internal error: inconsistent I/O"
}
}
}
pri func decoder.read_from!(src: base.io_reader) {
var clear_code : base.u32[..= 256]
var end_code : base.u32[..= 257]
var save_code : base.u32[..= 4096]
var prev_code : base.u32[..= 4095]
var width : base.u32[..= 12]
var bits : base.u32
var n_bits : base.u32[..= 31]
var output_wi : base.u32[..= 8191]
var code : base.u32[..= 4095]
var c : base.u32[..= 4095]
var o : base.u32[..= 8191]
var steps : base.u32
var first_byte : base.u8
var lm1_b : base.u16[..= 4095]
var lm1_a : base.u16[..= 4095]
clear_code = this.clear_code
end_code = this.end_code
save_code = this.save_code
prev_code = this.prev_code
width = this.width
bits = this.bits
n_bits = this.n_bits
output_wi = this.output_wi
while true {
if n_bits < width {
assert n_bits < 12 via "a < b: a < c; c <= b"(c: width)
if args.src.available() >= 4 {
// Read 4 bytes, using the "Variant 4" technique of
// https://fgiesen.wordpress.com/2018/02/20/reading-bits-in-far-too-many-ways-part-2/
bits |= args.src.peek_u32le() ~mod<< n_bits
args.src.skip_fast!(actual: (31 - n_bits) >> 3, worst_case: 3)
n_bits |= 24
assert width <= n_bits via "a <= b: a <= c; c <= b"(c: 12)
assert n_bits >= width via "a >= b: b <= a"()
} else if args.src.available() <= 0 {
this.read_from_return_value = 2
break
} else {
bits |= args.src.peek_u8_as_u32() << n_bits
args.src.skip_fast!(actual: 1, worst_case: 1)
n_bits += 8
if n_bits >= width {
// No-op.
} else if args.src.available() <= 0 {
this.read_from_return_value = 2
break
} else {
bits |= args.src.peek_u8_as_u32() << n_bits
args.src.skip_fast!(actual: 1, worst_case: 1)
n_bits += 8
assert width <= n_bits via "a <= b: a <= c; c <= b"(c: 12)
assert n_bits >= width via "a >= b: b <= a"()
// This if condition is always false, but for some unknown
// reason, removing it worsens the benchmarks slightly.
if n_bits < width {
this.read_from_return_value = 4
break
}
}
}
}
code = bits.low_bits(n: width)
bits >>= width
n_bits -= width
if code < clear_code {
assert code < 256 via "a < b: a < c; c <= b"(c: clear_code)
this.output[output_wi] = code as base.u8
output_wi = (output_wi + 1) & 8191
if save_code <= 4095 {
lm1_a = (this.lm1s[prev_code] ~mod+ 1) & 4095
this.lm1s[save_code] = lm1_a
if (lm1_a % 8) <> 0 {
this.prefixes[save_code] = this.prefixes[prev_code]
this.suffixes[save_code] = this.suffixes[prev_code]
this.suffixes[save_code][lm1_a % 8] = code as base.u8
} else {
this.prefixes[save_code] = prev_code as base.u16
this.suffixes[save_code][0] = code as base.u8
}
save_code += 1
if width < 12 {
width += 1 & (save_code >> width)
}
prev_code = code
}
} else if code <= end_code {
if code == end_code {
this.read_from_return_value = 0
break
}
save_code = end_code
prev_code = end_code
width = this.literal_width + 1
} else if code <= save_code {
c = code
if code == save_code {
c = prev_code
}
// Letting old_wi and new_wi denote the values of output_wi before
// and after these two lines of code, the decoded bytes will be
// written to output[old_wi:new_wi]. They will be written
// back-to-front, 8 bytes at a time, starting by writing
// output[o:o + 8], which will contain output[new_wi - 1].
//
// In the special case that code == save_code, the decoded bytes
// contain an extra copy (at the end) of the first byte, and will
// be written to output[old_wi:new_wi + 1].
o = (output_wi + ((this.lm1s[c] as base.u32) & 0xFFFFFFF8)) & 8191
output_wi = (output_wi + 1 + (this.lm1s[c] as base.u32)) & 8191
steps = (this.lm1s[c] as base.u32) >> 3
while true {
assert o <= (o + 8) via "a <= (a + b): 0 <= b"(b: 8)
// The final "8" is redundant semantically, but helps the
// wuffs-c code generator recognize that both slices have the
// same constant length, and hence produce efficient C code.
this.output[o .. o + 8].copy_from_slice!(s: this.suffixes[c][.. 8])
if steps <= 0 {
break
}
steps -= 1
// This line is essentially "o -= 8". The "& 8191" is a no-op
// in practice, but is necessary for the overflow checker.
o = (o ~mod- 8) & 8191
c = this.prefixes[c] as base.u32
}
first_byte = this.suffixes[c][0]
if code == save_code {
this.output[output_wi] = first_byte
output_wi = (output_wi + 1) & 8191
}
if save_code <= 4095 {
lm1_b = (this.lm1s[prev_code] ~mod+ 1) & 4095
this.lm1s[save_code] = lm1_b
if (lm1_b % 8) <> 0 {
this.prefixes[save_code] = this.prefixes[prev_code]
this.suffixes[save_code] = this.suffixes[prev_code]
this.suffixes[save_code][lm1_b % 8] = first_byte
} else {
this.prefixes[save_code] = prev_code as base.u16
this.suffixes[save_code][0] = first_byte as base.u8
}
save_code += 1
if width < 12 {
width += 1 & (save_code >> width)
}
prev_code = code
}
} else {
this.read_from_return_value = 3
break
}
// Flush the output if it could be too full to contain the entire
// decoding of the next code. The longest possible decoding is slightly
// less than 4096 and output's length is 8192, so a conservative
// threshold is ensuring that output_wi <= 4095.
if output_wi > 4095 {
this.read_from_return_value = 1
break
}
}
// Rewind args.src, if we're not in "$short read" and we've read too many
// bits.
if this.read_from_return_value <> 2 {
while n_bits >= 8 {
n_bits -= 8
if args.src.can_undo_byte() {
args.src.undo_byte!()
} else {
this.read_from_return_value = 4
break
}
}
}
this.save_code = save_code
this.prev_code = prev_code
this.width = width
this.bits = bits
this.n_bits = n_bits
this.output_wi = output_wi
}
pri func decoder.write_to?(dst: base.io_writer) {
var s : slice base.u8
var n : base.u64
while this.output_wi > 0 {
if this.output_ri > this.output_wi {
return "#internal error: inconsistent I/O"
}
s = this.output[this.output_ri .. this.output_wi]
n = args.dst.copy_from_slice!(s: s)
if n == s.length() {
this.output_ri = 0
this.output_wi = 0
return ok
}
this.output_ri = (this.output_ri ~mod+ ((n & 0xFFFFFFFF) as base.u32)) & 8191
yield? base."$short write"
}
}
pub func decoder.flush!() slice base.u8 {
var s : slice base.u8
if this.output_ri <= this.output_wi {
s = this.output[this.output_ri .. this.output_wi]
}
this.output_ri = 0
this.output_wi = 0
return s
}