broken code

rabin.go

package rabin

import (
	"bufio"
	"bytes"
	"crypto/rand"
	"fmt"
	"io"
	"testing"
)

func ThisMightBeRabin(r io.Reader) chan []byte {
	out := make(chan []byte)
	go func() {
		// Buffer input
		inbuf := bufio.NewReader(r)
		blkbuf := new(bytes.Buffer)

		// Some random bullshit numbers i made up
		a := 10
		mask := 0xfff
		MOD := 33554383
		windowSize := 16
		an := 1
		rollingHash := 0

		// Window is a circular buffer
		window := make([]byte, windowSize)
		get := func(i int) int { return int(window[i%len(window)]) }
		set := func(i int, val byte) { window[i%len(window)] = val }

		// Read in window length
		i := 0
		for ; i < windowSize; i++ {
			b, err := inbuf.ReadByte()
			if err != nil {
				fmt.Println(err)
				return
			}
			blkbuf.WriteByte(b)
			window[i] = b
			rollingHash = (rollingHash*a + int(b)) % MOD
			an = (an * a) % MOD
		}

		// Compute rolling hashes
		for ; true; i++ {
			b, err := inbuf.ReadByte()
			if err != nil {
				break
			}
			outval := get(i)
			set(i, b)
			blkbuf.WriteByte(b)
			rollingHash = (rollingHash*a + get(i) - an*outval) % MOD

			if rollingHash&mask == mask {
				fmt.Printf("sending buf: %v\n", blkbuf.Bytes()[:16])
				out <- blkbuf.Bytes()
				blkbuf.Reset()
			}
			peek, err := inbuf.Peek(windowSize)
			if err != nil || len(peek) != windowSize {
				break
			}
		}
		io.Copy(blkbuf, inbuf)
		fmt.Printf("sending last buf: %v\n", blkbuf.Bytes()[:16])
		out <- blkbuf.Bytes()
		close(out)
	}()
	return out
}

func TestRabinSplit(t *testing.T) {

	// Generate some random data
	nbytes := 256 * 4096
	buf := new(bytes.Buffer)
	io.CopyN(buf, rand.Reader, int64(nbytes))
	good := buf.Bytes()

	// Get Block Generator for random data
	ch := ThisMightBeRabin(buf)

	i := 0
	var blocks [][]byte
	for blk := range ch {
		fmt.Printf("got block: %v\n", blk[:16])
		if !bytes.Equal(blk, good[i:len(blk)+i]) {
			t.Fatalf("bad block! %v", blk[:16])
		} else {
			fmt.Println("GOOD BLOCK MATE!")
		}
		i += len(blk)
		blocks = append(blocks, blk)
	}
}