Switch to div_ceil for rounding implementation

src/decoder/image.rs

@@ -29,10 +29,10 @@ pub(crate) struct TileAttributes {
 
 impl TileAttributes {
     pub fn tiles_across(&self) -> usize {
-        (self.image_width + self.tile_width - 1) / self.tile_width
+        self.image_width.div_ceil(self.tile_width)
     }
     pub fn tiles_down(&self) -> usize {
-        (self.image_height + self.tile_length - 1) / self.tile_length
+        self.image_height.div_ceil(self.tile_length)
     }
     fn padding_right(&self) -> usize {
         (self.tile_width - self.image_width % self.tile_width) % self.tile_width
@@ -625,12 +625,12 @@ impl Image {
         let chunk_row_bits = (u64::from(chunk_dims.0) * u64::from(self.bits_per_sample))
             .checked_mul(samples as u64)
             .ok_or(TiffError::LimitsExceeded)?;
-        let chunk_row_bytes: usize = ((chunk_row_bits + 7) / 8).try_into()?;
+        let chunk_row_bytes: usize = chunk_row_bits.div_ceil(8).try_into()?;
 
         let data_row_bits = (u64::from(data_dims.0) * u64::from(self.bits_per_sample))
             .checked_mul(samples as u64)
             .ok_or(TiffError::LimitsExceeded)?;
-        let data_row_bytes: usize = ((data_row_bits + 7) / 8).try_into()?;
+        let data_row_bytes: usize = data_row_bits.div_ceil(8).try_into()?;
 
         // TODO: Should these return errors instead?
         assert!(output_row_stride >= data_row_bytes);