if err := os.WriteFile("impl.go", out, 0660); err != nil {
		log.Fatal(err)
	}
}

const pre = `// Code generated by go run gen.go; DO NOT EDIT.

package imageutil

import (
	"image"
)

// DrawYCbCr draws the YCbCr source image on the RGBA destination image with
// r.Min in dst aligned with sp in src. It reports whether the draw was
// successful. If it returns false, no dst pixels were changed.
//

// Code generated by go run gen.go; DO NOT EDIT.

package imageutil

import (
	"image"
)

// DrawYCbCr draws the YCbCr source image on the RGBA destination image with
// r.Min in dst aligned with sp in src. It reports whether the draw was
// successful. If it returns false, no dst pixels were changed.
//
// This function assumes that r is entirely within dst's bounds and the
// translation of r from dst coordinate space to src coordinate space is

					// An image.YCbCr is always fully opaque, and so if the
					// mask is nil (i.e. fully opaque) then the op is
					// effectively always Src. Similarly for image.Gray and
					// image.CMYK.
					if imageutil.DrawYCbCr(dst0, r, src0, sp) {
						return
					}
				case *image.Gray:
					drawGray(dst0, r, src0, sp)
					return
				case *image.CMYK:
					drawCMYK(dst0, r, src0, sp)
					return
				}

		// out the 'Adobe inversion' described in the applyBlack doc comment
		// above, so in practice, only the fourth channel (black) is inverted.
		bounds := d.img3.Bounds()
		img := image.NewRGBA(bounds)
		imageutil.DrawYCbCr(img, bounds, d.img3, bounds.Min)
		for iBase, y := 0, bounds.Min.Y; y < bounds.Max.Y; iBase, y = iBase+img.Stride, y+1 {
			for i, x := iBase+3, bounds.Min.X; x < bounds.Max.X; i, x = i+4, x+1 {