From 9faac7e1cacc1787bd45987c0f28b5aa1fbb9563 Mon Sep 17 00:00:00 2001
From: pommicket <pommicket@gmail.com>
Date: Mon, 8 Sep 2025 14:45:29 -0400
Subject: Various code cleanup

---
 src/lib.rs | 39 ++++++++++++++++-----------------------
 1 file changed, 16 insertions(+), 23 deletions(-)

(limited to 'src/lib.rs')

diff --git a/src/lib.rs b/src/lib.rs
index 9d61021..dc8ee83 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -322,8 +322,8 @@ impl ImageHeader {
 	pub fn bytes_per_row(&self) -> usize {
 		(self.width() as usize
 			* usize::from(self.bit_depth() as u8)
-			* usize::from(self.color_type().channels())
-			+ 7) / 8
+			* usize::from(self.color_type().channels()))
+		.div_ceil(8)
 	}
 
 	fn data_size(&self) -> usize {
@@ -375,7 +375,7 @@ impl BitReader<'_> {
 	}
 
 	fn peek_bits(&mut self, count: u8) -> Result<u32> {
-		debug_assert!(count > 0 && u32::from(count) <= 31);
+		debug_assert!(count > 0 && count <= 31);
 		if self.bits_left < count {
 			self.read_more_bits()?;
 		}
@@ -433,7 +433,7 @@ impl<'a> From<&'a mut [u8]> for DecompressedDataWriter<'a> {
 	}
 }
 
-impl<'a> DecompressedDataWriter<'a> {
+impl DecompressedDataWriter<'_> {
 	fn write_byte(&mut self, byte: u8) -> Result<()> {
 		match self.slice.get_mut(self.pos) {
 			None => return Err(Error::TooMuchData),
@@ -527,7 +527,7 @@ impl HuffmanTable {
 					*entry = -i;
 				} else {
 					debug_assert!(*entry < 0);
-				};
+				}
 				entry = &mut self.tree[usize::from((-*entry) as u16 + (code & 1))];
 				code >>= 1;
 			}
@@ -963,12 +963,6 @@ fn read_compressed_block(
 	writer: &mut DecompressedDataWriter,
 	dynamic: bool,
 ) -> Result<()> {
-	let (literal_length_table, distance_table) = if dynamic {
-		read_dynamic_huffman_dictionary(reader)?
-	} else {
-		get_fixed_huffman_dictionaries()
-	};
-
 	fn parse_length(reader: &mut BitReader, literal_length: u16) -> Result<u16> {
 		Ok(match literal_length {
 			257..=264 => literal_length - 254,
@@ -1004,6 +998,12 @@ fn read_compressed_block(
 		})
 	}
 
+	let (literal_length_table, distance_table) = if dynamic {
+		read_dynamic_huffman_dictionary(reader)?
+	} else {
+		get_fixed_huffman_dictionaries()
+	};
+
 	loop {
 		let literal_length = literal_length_table.read_value(reader)?;
 		match literal_length {
@@ -1090,6 +1090,7 @@ fn read_image(reader: IdatReader, writer: &mut DecompressedDataWriter) -> Result
 	}
 
 	if cfg!(feature = "adler") {
+		const BASE: u32 = 65521;
 		// Adler-32 checksum
 		let padding = reader.bits_left % 8;
 		if padding > 0 {
@@ -1101,7 +1102,6 @@ fn read_image(reader: IdatReader, writer: &mut DecompressedDataWriter) -> Result
 		expected_adler |= reader.read_bits(16)? << 16;
 		expected_adler = expected_adler.swap_bytes();
 
-		const BASE: u32 = 65521;
 		let mut s1: u32 = 1;
 		let mut s2: u32 = 0;
 		for byte in writer.slice[..decompressed_size].iter().copied() {
@@ -1136,18 +1136,18 @@ fn apply_filters(header: &ImageHeader, data: &mut [u8]) -> Result<()> {
 	);
 	let scanline_bytes = header.bytes_per_row();
 	for scanline in 0..header.height() {
-		let filter = data[s];
 		const FILTER_NONE: u8 = 0;
 		const FILTER_SUB: u8 = 1;
 		const FILTER_UP: u8 = 2;
 		const FILTER_AVG: u8 = 3;
 		const FILTER_PAETH: u8 = 4;
+		let filter = data[s];
 
 		s += 1;
 		data.copy_within(s..s + scanline_bytes, d);
 		match (filter, scanline == 0) {
 			(FILTER_NONE, _) | (FILTER_UP, true) => {}
-			(FILTER_SUB, _) => {
+			(FILTER_SUB, _) | (FILTER_PAETH, true) => {
 				for i in d + x_byte_offset..d + scanline_bytes {
 					data[i] = data[i].wrapping_add(data[i - x_byte_offset]);
 				}
@@ -1162,10 +1162,8 @@ fn apply_filters(header: &ImageHeader, data: &mut [u8]) -> Result<()> {
 					data[i] = data[i].wrapping_add(data[i - scanline_bytes] / 2);
 				}
 				for i in d + x_byte_offset..d + scanline_bytes {
-					data[i] = data[i].wrapping_add(
-						((u32::from(data[i - scanline_bytes]) + u32::from(data[i - x_byte_offset]))
-							/ 2) as u8,
-					);
+					data[i] = data[i]
+						.wrapping_add(data[i - scanline_bytes].midpoint(data[i - x_byte_offset]));
 				}
 			}
 			(FILTER_AVG, true) => {
@@ -1196,11 +1194,6 @@ fn apply_filters(header: &ImageHeader, data: &mut [u8]) -> Result<()> {
 					data[i] = data[i].wrapping_add(paeth);
 				}
 			}
-			(FILTER_PAETH, true) => {
-				for i in d + x_byte_offset..d + scanline_bytes {
-					data[i] = data[i].wrapping_add(data[i - x_byte_offset]);
-				}
-			}
 			(5.., _) => return Err(Error::BadFilter),
 		}
 
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