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path: root/trie/encoding.go
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Diffstat (limited to 'trie/encoding.go')
-rw-r--r--trie/encoding.go114
1 files changed, 50 insertions, 64 deletions
diff --git a/trie/encoding.go b/trie/encoding.go
index 2037118dd..e96a786e4 100644
--- a/trie/encoding.go
+++ b/trie/encoding.go
@@ -16,49 +16,54 @@
package trie
-func compactEncode(hexSlice []byte) []byte {
+// Trie keys are dealt with in three distinct encodings:
+//
+// KEYBYTES encoding contains the actual key and nothing else. This encoding is the
+// input to most API functions.
+//
+// HEX encoding contains one byte for each nibble of the key and an optional trailing
+// 'terminator' byte of value 0x10 which indicates whether or not the node at the key
+// contains a value. Hex key encoding is used for nodes loaded in memory because it's
+// convenient to access.
+//
+// COMPACT encoding is defined by the Ethereum Yellow Paper (it's called "hex prefix
+// encoding" there) and contains the bytes of the key and a flag. The high nibble of the
+// first byte contains the flag; the lowest bit encoding the oddness of the length and
+// the second-lowest encoding whether the node at the key is a value node. The low nibble
+// of the first byte is zero in the case of an even number of nibbles and the first nibble
+// in the case of an odd number. All remaining nibbles (now an even number) fit properly
+// into the remaining bytes. Compact encoding is used for nodes stored on disk.
+
+func hexToCompact(hex []byte) []byte {
terminator := byte(0)
- if hexSlice[len(hexSlice)-1] == 16 {
+ if hasTerm(hex) {
terminator = 1
- hexSlice = hexSlice[:len(hexSlice)-1]
- }
- var (
- odd = byte(len(hexSlice) % 2)
- buflen = len(hexSlice)/2 + 1
- bi, hi = 0, 0 // indices
- hs = byte(0) // shift: flips between 0 and 4
- )
- if odd == 0 {
- bi = 1
- hs = 4
+ hex = hex[:len(hex)-1]
}
- buf := make([]byte, buflen)
- buf[0] = terminator<<5 | byte(odd)<<4
- for bi < len(buf) && hi < len(hexSlice) {
- buf[bi] |= hexSlice[hi] << hs
- if hs == 0 {
- bi++
- }
- hi, hs = hi+1, hs^(1<<2)
+ buf := make([]byte, len(hex)/2+1)
+ buf[0] = terminator << 5 // the flag byte
+ if len(hex)&1 == 1 {
+ buf[0] |= 1 << 4 // odd flag
+ buf[0] |= hex[0] // first nibble is contained in the first byte
+ hex = hex[1:]
}
+ decodeNibbles(hex, buf[1:])
return buf
}
-func compactDecode(str []byte) []byte {
- base := compactHexDecode(str)
+func compactToHex(compact []byte) []byte {
+ base := keybytesToHex(compact)
base = base[:len(base)-1]
+ // apply terminator flag
if base[0] >= 2 {
base = append(base, 16)
}
- if base[0]%2 == 1 {
- base = base[1:]
- } else {
- base = base[2:]
- }
- return base
+ // apply odd flag
+ chop := 2 - base[0]&1
+ return base[chop:]
}
-func compactHexDecode(str []byte) []byte {
+func keybytesToHex(str []byte) []byte {
l := len(str)*2 + 1
var nibbles = make([]byte, l)
for i, b := range str {
@@ -69,35 +74,24 @@ func compactHexDecode(str []byte) []byte {
return nibbles
}
-// compactHexEncode encodes a series of nibbles into a byte array
-func compactHexEncode(nibbles []byte) []byte {
- nl := len(nibbles)
- if nl == 0 {
- return nil
- }
- if nibbles[nl-1] == 16 {
- nl--
+// hexToKeybytes turns hex nibbles into key bytes.
+// This can only be used for keys of even length.
+func hexToKeybytes(hex []byte) []byte {
+ if hasTerm(hex) {
+ hex = hex[:len(hex)-1]
}
- l := (nl + 1) / 2
- var str = make([]byte, l)
- for i := range str {
- b := nibbles[i*2] * 16
- if nl > i*2 {
- b += nibbles[i*2+1]
- }
- str[i] = b
+ if len(hex)&1 != 0 {
+ panic("can't convert hex key of odd length")
}
- return str
+ key := make([]byte, (len(hex)+1)/2)
+ decodeNibbles(hex, key)
+ return key
}
-func decodeCompact(key []byte) []byte {
- l := len(key) / 2
- var res = make([]byte, l)
- for i := 0; i < l; i++ {
- v1, v0 := key[2*i], key[2*i+1]
- res[i] = v1*16 + v0
+func decodeNibbles(nibbles []byte, bytes []byte) {
+ for bi, ni := 0, 0; ni < len(nibbles); bi, ni = bi+1, ni+2 {
+ bytes[bi] = nibbles[ni]<<4 | nibbles[ni+1]
}
- return res
}
// prefixLen returns the length of the common prefix of a and b.
@@ -114,15 +108,7 @@ func prefixLen(a, b []byte) int {
return i
}
+// hasTerm returns whether a hex key has the terminator flag.
func hasTerm(s []byte) bool {
- return s[len(s)-1] == 16
-}
-
-func remTerm(s []byte) []byte {
- if hasTerm(s) {
- b := make([]byte, len(s)-1)
- copy(b, s)
- return b
- }
- return s
+ return len(s) > 0 && s[len(s)-1] == 16
}