chunker: Use polynomial functions
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8986c75091
commit
f02865a205
2 changed files with 17 additions and 42 deletions
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@ -25,8 +25,8 @@ const (
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)
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type tables struct {
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out [256]uint64
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mod [256]uint64
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out [256]Pol
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mod [256]Pol
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}
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// cache precomputed tables, these are read-only anyway
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@ -151,13 +151,13 @@ func (c *Chunker) fill_tables() {
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//
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// Afterwards a new byte can be shifted in.
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for b := 0; b < 256; b++ {
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var hash uint64
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var h Pol
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hash = append_byte(hash, byte(b), uint64(c.pol))
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h = append_byte(h, byte(b), c.pol)
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for i := 0; i < WindowSize-1; i++ {
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hash = append_byte(hash, 0, uint64(c.pol))
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h = append_byte(h, 0, c.pol)
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}
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c.tables.out[b] = hash
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c.tables.out[b] = h
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}
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// calculate table for reduction mod Polynomial
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@ -170,7 +170,7 @@ func (c *Chunker) fill_tables() {
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// two parts: Part A contains the result of the modulus operation, part
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// B is used to cancel out the 8 top bits so that one XOR operation is
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// enough to reduce modulo Polynomial
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c.tables.mod[b] = mod(uint64(b)<<uint(k), uint64(c.pol)) | (uint64(b) << uint(k))
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c.tables.mod[b] = Pol(uint64(b)<<uint(k)).Mod(c.pol) | (Pol(b) << uint(k))
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}
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}
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@ -245,7 +245,7 @@ func (c *Chunker) Next() (*Chunk, error) {
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// inline c.slide(b) and append(b) to increase performance
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out := c.window[c.wpos]
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c.window[c.wpos] = b
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c.digest ^= c.tables.out[out]
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c.digest ^= uint64(c.tables.out[out])
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c.wpos = (c.wpos + 1) % WindowSize
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// c.append(b)
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@ -253,7 +253,7 @@ func (c *Chunker) Next() (*Chunk, error) {
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c.digest <<= 8
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c.digest |= uint64(b)
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c.digest ^= c.tables.mod[index]
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c.digest ^= uint64(c.tables.mod[index])
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// end inline
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add++
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@ -323,48 +323,21 @@ func (c *Chunker) append(b byte) {
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c.digest <<= 8
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c.digest |= uint64(b)
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c.digest ^= c.tables.mod[index]
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c.digest ^= uint64(c.tables.mod[index])
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}
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func (c *Chunker) slide(b byte) {
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out := c.window[c.wpos]
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c.window[c.wpos] = b
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c.digest ^= c.tables.out[out]
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c.digest ^= uint64(c.tables.out[out])
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c.wpos = (c.wpos + 1) % WindowSize
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c.append(b)
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}
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func append_byte(hash uint64, b byte, pol uint64) uint64 {
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func append_byte(hash Pol, b byte, pol Pol) Pol {
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hash <<= 8
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hash |= uint64(b)
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hash |= Pol(b)
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return mod(hash, pol)
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}
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// Mod calculates the remainder of x divided by p in F_2[X].
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func mod(x, p uint64) uint64 {
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for deg(x) >= deg(p) {
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shift := uint(deg(x) - deg(p))
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x = x ^ (p << shift)
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}
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return x
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}
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// Deg returns the degree of the polynomial p, this is equivalent to the number
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// of the highest bit set in p.
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func deg(p uint64) int {
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var mask uint64 = 0x8000000000000000
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for i := 0; i < 64; i++ {
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if mask&p > 0 {
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return 63 - i
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}
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mask >>= 1
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}
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return -1
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return hash.Mod(pol)
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}
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@ -64,12 +64,14 @@ func (x Pol) Deg() int {
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return -1
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}
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var mask Pol = (1 << 63)
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for i := 63; i >= 0; i-- {
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// test if bit i is set
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if x&(1<<uint(i)) > 0 {
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if x&mask > 0 {
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// this is the degree of x
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return i
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}
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mask >>= 1
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}
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// fall-through, return -1
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