filetab := f.pcfile()
		linetab := f.pcln()
		if t.version == ver116 || t.version == ver118 || t.version == ver120 {
			if f.cuOffset() == ^uint32(0) {
				// skip functions without compilation unit (not real function, or linker generated)
				continue
			}
			cutab = t.cutab[f.cuOffset()*4:]
		}
		pc := t.findFileLine(entry, filetab, linetab, int32(filenum), int32(line), cutab)
		if pc != 0 {
			return pc
		}

	textStart      uintptr // base for function entry PC offsets in this module, equal to moduledata.text
	funcnameOffset uintptr // offset to the funcnametab variable from pcHeader
	cuOffset       uintptr // offset to the cutab variable from pcHeader
	filetabOffset  uintptr // offset to the filetab variable from pcHeader
	pctabOffset    uintptr // offset to the pctab variable from pcHeader

	// Calculate the size of the runtime.cutab variable.
	var totalEntries uint32
	cuOffsets := make([]uint32, len(cuEntries))
	for i, entries := range cuEntries {
		// Note, cutab is a slice of uint32, so an offset to a cu's entry is just the
		// running total of all cu indices we've needed to store so far, not the
		// number of bytes we've stored so far.
		cuOffsets[i] = totalEntries
		totalEntries += uint32(entries)
	}

	args        int32  // in/out args size
	deferreturn uint32 // offset of start of a deferreturn call instruction from entry, if any.

	pcsp      uint32
	pcfile    uint32
	pcln      uint32
	npcdata   uint32
	cuOffset  uint32     // runtime.cutab offset of this function's CU
	startLine int32      // line number of start of function (func keyword/TEXT directive)
	funcID    abi.FuncID // set for certain special runtime functions

		return color.YCbCr{}
	}
	yi := p.YOffset(x, y)
	ci := p.COffset(x, y)
	return color.YCbCr{
		p.Y[yi],
		p.Cb[ci],
		p.Cr[ci],
	}
}

// YOffset returns the index of the first element of Y that corresponds to
// the pixel at (x, y).
func (p *YCbCr) YOffset(x, y int) int {
	return (y-p.Rect.Min.Y)*p.YStride + (x - p.Rect.Min.X)
}

// COffset returns the index of the first element of Cb or Cr that corresponds

			col := color.RGBA{
				uint8(rnd.Intn(256)),
				uint8(rnd.Intn(256)),
				uint8(rnd.Intn(256)),
				255,
			}
			imgRGBA.SetRGBA(x, y, col)
			yo := imgYCbCr.YOffset(x, y)
			co := imgYCbCr.COffset(x, y)
			cy, ccr, ccb := color.RGBToYCbCr(col.R, col.G, col.B)
			imgYCbCr.Y[yo] = cy
			imgYCbCr.Cb[co] = ccr
			imgYCbCr.Cr[co] = ccb
		}
	}

	// Now check that both images are identical after an encode.

	// will be set multiple times. That's OK. We just want to avoid a uniform image.
	for y := r1.Min.Y; y < r1.Max.Y; y++ {
		for x := r1.Min.X; x < r1.Max.X; x++ {
			yi := m.YOffset(x, y)
			ci := m.COffset(x, y)
			m.Y[yi] = uint8(16*y + x)
			m.Cb[ci] = uint8(y + 16*x)
			m.Cr[ci] = uint8(y + 16*x)
		}
	}

	// Make various sub-images of m.
	for y0 := delta.Y + 3; y0 < delta.Y+7; y0++ {

		return 0, err
	}
	defer fd.decref()

	if len(b) > maxRW {
		b = b[:maxRW]
	}

	fd.l.Lock()
	defer fd.l.Unlock()
	curoffset, e := syscall.Seek(fd.Sysfd, 0, io.SeekCurrent)
	if e != nil {
		return 0, e
	}
	defer syscall.Seek(fd.Sysfd, curoffset, io.SeekStart)
	o := syscall.Overlapped{
		OffsetHigh: uint32(off >> 32),
		Offset:     uint32(off),
	}
	var done uint32

pkg image, method (*NYCbCrA) AOffset(int, int) int
pkg image, method (*NYCbCrA) At(int, int) color.Color
pkg image, method (*NYCbCrA) Bounds() Rectangle
pkg image, method (*NYCbCrA) COffset(int, int) int
pkg image, method (*NYCbCrA) ColorModel() color.Model
pkg image, method (*NYCbCrA) NYCbCrAAt(int, int) color.NYCbCrA
pkg image, method (*NYCbCrA) Opaque() bool

		sy := p.Y + j
		if sy > ymax {
			sy = ymax
		}
		for i := 0; i < 8; i++ {
			sx := p.X + i
			if sx > xmax {
				sx = xmax
			}
			yi := m.YOffset(sx, sy)
			ci := m.COffset(sx, sy)
			yBlock[8*j+i] = int32(m.Y[yi])
			cbBlock[8*j+i] = int32(m.Cb[ci])
			crBlock[8*j+i] = int32(m.Cr[ci])
		}
	}
}

// scale scales the 16x16 region represented by the 4 src blocks to the 8x8