std/bzip2/decode_flush_slow.wuffs

// Copyright 2022 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.

pri func decoder.flush_block?(dst: base.io_writer) {
	var i                   : base.u32[..= 1_048575]
	var n                   : base.u32
	var entry               : base.u32
	var repeat_count        : base.u32[..= 255]
	var block_checksum_have : base.u32
	var prev                : base.u8
	var curr                : base.u8

	if this.original_pointer >= this.block_size {
		return "#bad block length"
	}
	assert this.original_pointer < 900000 via "a < b: a < c; c <= b"(c: this.block_size)
	i = this.bwt[this.original_pointer] >> 12

	block_checksum_have = 0xFFFF_FFFF

	n = 0
	while n < this.block_size {
		assert n < 900000 via "a < b: a < c; c <= b"(c: this.block_size)
		entry = this.bwt[i]
		curr = (entry & 0xFF) as base.u8
		i = entry >> 12

		if repeat_count >= 4 {
			repeat_count = curr as base.u32
			while repeat_count > 0,
				inv n < 900000,
			{
				block_checksum_have =
					REV_CRC32_TABLE[((block_checksum_have >> 24) as base.u8) ^ prev] ^
					(block_checksum_have ~mod<< 8)
				args.dst.write_u8?(a: prev)
				repeat_count -= 1
			} endwhile
			repeat_count = 0
		} else if curr <> prev {
			repeat_count = 1
			block_checksum_have =
				REV_CRC32_TABLE[((block_checksum_have >> 24) as base.u8) ^ curr] ^
				(block_checksum_have ~mod<< 8)
			args.dst.write_u8?(a: curr)
		} else {
			repeat_count += 1
			block_checksum_have =
				REV_CRC32_TABLE[((block_checksum_have >> 24) as base.u8) ^ curr] ^
				(block_checksum_have ~mod<< 8)
			args.dst.write_u8?(a: curr)
		}

		prev = curr
		n += 1
	} endwhile

	block_checksum_have ^= 0xFFFF_FFFF
	if block_checksum_have <> this.block_checksum_want {
		return "#bad checksum"
	}
	this.final_checksum_have = block_checksum_have ^ (
		(this.final_checksum_have >> 31) |
		(this.final_checksum_have ~mod<< 1))
}