Fix libmegapixels_mode_width_to_bytes/libmegapixels_mode_width_to_padding for non-8bit formats

src/mode.c

@@ -306,31 +306,33 @@ libmegapixels_format_cfa_pattern(int format)
 	}
 }
 
-// mp_pixel_format_width_to_bytes
+/* Calculates the number of bytes required to store a row of pixels for a given mode and width. */
 uint32_t
 libmegapixels_mode_width_to_bytes(int index, uint32_t width)
 {
 	uint32_t bits_per_pixel = mode_lut[index].bpp;
 	uint64_t bits_per_width = width * (uint64_t) bits_per_pixel;
 	uint64_t remainder = bits_per_width % 8;
+	uint32_t result = 0;
 	if (remainder == 0)
-		return bits_per_width / 8;
+		result = bits_per_width / 8;
+	else
+		result = (bits_per_width + 8 - remainder) / 8;
 
-	return (bits_per_width + 8 - remainder) / 8;
+	return result;
 }
 
+/* Calculates the padding (in bytes) required at the end of each row for a given mode and width. */
 uint32_t
 libmegapixels_mode_width_to_padding(int index, uint32_t width)
 {
-	if (mode_lut[index].bpp == 8) {
-		return 0;
-	}
-	uint64_t bytes_per_width = libmegapixels_mode_width_to_bytes(index, width);
-	uint64_t remainder = bytes_per_width % 8;
+	int remainder = mode_lut[index].bpp % 8;
 	if (remainder == 0)
-		return remainder;
+		return 0;
+
+	uint32_t padding = ((uint64_t) (8 - remainder) * width) / 8;
 
-	return 8 - remainder;
+	return padding;
 }
 
 uint32_t