Revert "optimize rot90c"

This reverts commit e2002f18b4.

src/affine.rs

@@ -105,18 +105,11 @@ impl<const CHANNELS: usize> ImageCloner<'_, CHANNELS> {
     /// UB if the image is not square
     #[must_use = "function does not modify the original image"]
     pub unsafe fn rot_90(&self) -> Image<Vec<u8>, CHANNELS> {
-        let mut o = self.alloc();
+        // SAFETY: yep
-        for y in 0..self.height() {
+        let mut out = unsafe { transpose_out(self) };
-            for x in 0..self.width() {
+        // SAFETY: sqar
-                // SAFETY: x and y in bounds, slice is okay
+        unsafe { crev(out.as_mut()) };
-                unsafe {
+        out
-                    let px = self.buffer.get_unchecked(self.slice(x, y));
-                    let out = o.pixel_mut(self.height() - y - 1, x);
-                    out.copy_from_slice(px);
-                }
-            }
-        }
-        o
     }
 
     /// Rotate an image 270 degrees clockwise, or 90 degrees anti clockwise.
@@ -163,6 +156,26 @@ impl<const CHANNELS: usize, T: AsMut<[u8]> + AsRef<[u8]>> Image<T, CHANNELS> {
     }
 }
 
+/// Reverse columns of square image
+/// # Safety
+///
+/// UB if supplied image not square
+unsafe fn crev<const CHANNELS: usize, T: AsMut<[u8]> + AsRef<[u8]>>(mut img: Image<T, CHANNELS>) {
+    debug_assert_eq!(img.width(), img.height());
+    let size = img.width() as usize;
+    let b = img.flatten_mut();
+    for i in 0..size {
+        let mut start = 0;
+        let mut end = size - 1;
+        while start < end {
+            // SAFETY: hmm
+            unsafe { b.swap_unchecked(i * size + start, i * size + end) };
+            start += 1;
+            end -= 1;
+        }
+    }
+}
+
 /// Transpose a square image out of place
 /// # Safety
 ///